I bought/would buy a 6D and not a D600 because...

[Canon-F1]

Well I shot Nikon for 25 years, and changed to FF Canon in 2005.

The change to Canon wasn't just driven by FF. Some of the things I found with the modern Nikons would be my reasons for choosing the 6D over the D600

These only relate to the prosumer grade of cameras:
Software that's a joke compared with Canon
Hideous plastic pop up flash
Rubber grip that peels away from the body
Rubber grip that binds the front command wheel
Soft lens mount that wears quickly and feels real slack with heavy lenses
Translucent LCD on focus screen makes manual focus horrid
Menus that I don't understand

And, the manual focus on Canon L lenses is superior to Nikon IME

In fact I have found that the Canon has a higher level of intrinsic quality to the equivalent Nikon.
Nikons are cheaper because they Are cheaper.

Don't take any notice of people who have called the 6D "cheap and plasticy". They will have never handled one.

Well said Sporgon. I didn't shoot Nikon for 25 years, but I shot a Nikon system long enough in the film era to be a dedicated fan at one point in time. About 6 years to be exact, something I can't deny or regret. It certainly helped me jumpstart my dedication to events coverage. However, I was attracted to Canon when I began to see all the white lenses in highly inspiring and motivational events like the Olympics, presidential campaigns, and at local sports games in my hometown of San Francisco. It certainly made me very curious. Deep down inside, I wanted the speed, accuracy, and color renditions of the rapidly improving EF lens lineup. However, what really broke me in half with Nikon was when Canon released the ever so popular 5D classic. Everyone who's shot DSLRs for at least close to a decade know how much of an impact this particular model made when it was announced, and even bigger when all of the jaw dropping photos turned up. I can't really say that I switched, but when I bought my 5D with a 50mm f/1.4 my Nikon F4 never saw the light of day again after that. I had to sell it and settle for a 40D at one point but I bought the classic again when the Mark II got released. I kept loyal to the 5D series, and backed it up with a 1D mark III for shooting weddings eventually. When the 5D mark III came out I just had to do a double take and convince my boss to buy another one because the AF is just so buttery smooth with Canon lenses when shooting events. Then the 6D came out... I have to admit, I was disappointed. Canon gives us this war beast called the 5D mark III and puts a little innocent kitty cat next to it called the 6D. So I thought... Okay.... maybe my wife will like it. Maybe we can take it on vacations because it's smaller and lighter. Okay...it's so hard to defend against the D600 specs but we already have a lot of Canon gear...

After reading around in the Nikon forums, then going to the store to hold a D600 and try it out, I was disappointed in how it felt in my hands. Like Sporgon, the menus drove me nuts. I tested it in the store with a Nikkor 50mm 1.8 (which to be fair, feels better than Canon's 50mm 1.8 II BTW) Looking at the horrible LCD screen made me laugh, because it made realize that I was a film photographer that has become a chimper. But if I'm going to chimp, the LCD screen better be good. The slight green tint didn't bother me as much as I thought it would when reading about it. However, the image was cropped inside of the screen to make room for the settings... Wow. Even if that could be changed, it's really not a good idea to put that on a camera as default. Anyways, at that point, it really didn't matter to me what the Nikon images would look like on a computer screen anymore. I was holding a camera that an event shooter would have a bit more trouble using compared to a Canon system and even compared to the way my old F4 was. I'm used to my brother's D7000 layout, which I hate, and wish they changed it in future bodies. But nope, they brought almost all of it back. Also after that experience I have enough reason to believe that the live view/video mode is horrible on Nikon cameras in general. I'm also a cinematographer, and I am still facepalmed for Nikon for simple tasks like changing settings while in live view. I suppose they think everyone owns an entire set of AF-D lenses. This is an important feature with the most basic of functions that should have worked straight out of the box, seamlessly. The frustrating button placements and situations that caused me to menu dive constantly were enough to turn me off on just the camera alone. They should have kept it simple! These are vital operation constraints. Good photographers should be spending less time on the science of fiddling with controls, and more time on the art.

So I pre-ordered a 6D for my wife. I wasn't excited, of course. Being used to the 5D mark III, it was really hard to see that anything could come close. Now we have two Canon 6D bodies.... One for me, because my wife wouldn't let go of hers for me to really shoot all day with it. But the reason I have one now... The first impression. Holding it is NOT like holding a 60D. (which I've also owned more than one body of, previously) I think that's the common misconception by the general public who look at the specs and photos of the camera and say oh, it's a full frame 60D. It is not. It's definitely heavier, feels like I have a better grip on it, and the control layout seems to make slightly better sense. You will definitely notice that it is better built than a 60D from when you first pick it up. I have exactly one issue with it that the 60D might have a tiny advantage in. And that's the fact I can't program the SET button to go directly to white balance settings. I have a dedicated white balance button in the 5D mark III, why not the 6D? However, I said tiny because you can program the SET button for quick menu, and throw white balance into the quick menu. One whole button press behind, not that big of a deal unless you're shooting in a moving vehicle that passes different light temperature conditions in which you are required to shoot in at 5mph or faster. Seriously.

The AF is not comparable to the 5D mark III at all, and everyone is right in the regards of believing the very obvious truth that it is in a different league in that regard. But that's why people are going to buy the 6D, because not everyone needs the 5D mark III. Nor do they all shoot in death defying extreme weather. Back to AF, the 6D is no slouch. I can easily say it's AF is better than both the 5D mark II and 5D classic. In fact, I feel like it focuses faster than the D600 when I have a good lens attached to it like the 135mm F2/L or my colleague's 70-200mm f/2.8L II. Which is not a fair comparison of course, since I only used the 50mm 1.8 on the D600. I won't get in too deep with lens performance, but it does sort of make me feel like Nikon marketing is just throwing more points on the D600 to compensate for some of their lower performing Nikon lenses compared to Canon lens equivalents. Which of course, isn't true and I'm just a Nikon basher right? ~_^ Okay, so Nikon seems to have the edge on outer points for moving subjects. But in my 3-4 weeks of experience with the 6D, I can at least say that the outer points are very much usable in good light and a target with enough contrast, but it disappointed me for moving subjects. Note, this is the same disappointment I had for the outer points on the 5D mark II and 5D classic. Also note, I didn't know I had this disappointment until I became dependent on 1D mark III and 5D mark III outer point AF. So, if you're used to the old 5D bodies, or even the old 9 point system on the XXD bodies, you won't really feel a difference. The center point, however, is a miracle worker. With just a macbook pro lighting the master bedroom and not even facing the subject, I can lock focus and photograph my sleeping wife despite the fact I was forced to use ISO51200 to expose correctly at a hand holdable shutter speed. I'll have to test the same situation with a 5D mark III, but I know for a fact that even my 1D mark III couldn't do that or would hunt for a bit before it thought it could. The fact I'm able to lock focus on any shot that requires ISO51200 when my 1D mark III couldn't do it at it's highest ISO of ISO6400 changes the game a bit in that regard. I'm shooting a local wedding soon, and I'm confident enough to try the 6D as a backup body to the 5D mark III and see how it does in a very poorly lit church.

For high ISO performance, and sometimes, the way the images just looked at all ISOs... I was disappointed too, initially. I looked at some of my old 5D mark II RAW files, and they were obviously sharper when viewing the image full on. However, the softer images didn't bother me anymore after I saw how well it handled sharpening in Lightroom and unsharp mask in Photoshop. I loaded my 5D classic RAW files, and a lot of the ISO100 files looked cleaner somehow which I'm sure is because of the weak AA filter and bigger pixels. A friend of mine sent me a couple of D600 RAW files from one of his events, and they looked just as flat as my 6D RAW files. A lot of this is accurate towards what the general consensus is saying around the net with their tests. However, I don't care about the 100% crop tests because I don't deliver 100% crops to my clients. After editing all the files, I found that the 6D RAW files looked better than both 5Ds and still had more realism to human skin tone compared to the D600 RAWs. I can still praise the D600 in this regard, because despite the slight preference in skin tone, the D600 RAW files are quite good. However, I'm still in agreement with Sporgon on the fact I am not willing to trade Canon's weaknesses for Nikon's weaknesses. It's like trying to drive a ferrari with helicopter controls, it doesn't matter how fast your car is if you can't get it from point A to point B. Perhaps overboard with the metaphor, but you know what I mean. Canon warranty is better as well, but I won't get in too deep with that either. (Seems like I got pretty deep with everything else though, lol)

The bottom line is, you have to make sure you're buying the cameras from a photographer's perspective if you want it to do everything you need it to do. Like many say, the camera's eco system including lens selection and accessories is much more important, so narrowing this all down to just cameras will prevent anyone from making a truly open minded decision. Like I said earlier, I'd rather spend more time on the art of photography. I'm not a camera engineer, that's the camera maker's job. Specs, operation, and sometimes rumors, though they are important factors, are just a supplement to what it all comes down to and that's a good photograph. We're not supposed to be on the computer all day zooming in and shaking fists about dynamic range, we're supposed to be out taking photos. That's why I can easily recommend the 6D over the D600, because I know for a fact it does the job and doesn't give me long term issues that could slow down or harm my workflow in the field. But in conclusion.... All I can say is..... Just buy a 5D Mark III if you can afford it

- Ryan

Thanks for your informative thoughts. Well said from someone who shot Nikon, the 5D series and the 6D as well... I was once a Nikon user myself but didn't like the Nikon ergonomics, its lens system and from where I am, its after sales services is no way better than Canon....

you don´t have to quote everything....   

[Bearcat1]

I chose the 6D because of the Wifi and the iPhone/IPad app. 

[verysimplejason]

Well I shot Nikon for 25 years, and changed to FF Canon in 2005.

The change to Canon wasn't just driven by FF. Some of the things I found with the modern Nikons would be my reasons for choosing the 6D over the D600

These only relate to the prosumer grade of cameras:
Software that's a joke compared with Canon
Hideous plastic pop up flash
Rubber grip that peels away from the body
Rubber grip that binds the front command wheel
Soft lens mount that wears quickly and feels real slack with heavy lenses
Translucent LCD on focus screen makes manual focus horrid
Menus that I don't understand

And, the manual focus on Canon L lenses is superior to Nikon IME

In fact I have found that the Canon has a higher level of intrinsic quality to the equivalent Nikon.
Nikons are cheaper because they Are cheaper.

Don't take any notice of people who have called the 6D "cheap and plasticy". They will have never handled one.

Well said Sporgon. I didn't shoot Nikon for 25 years, but I shot a Nikon system long enough in the film era to be a dedicated fan at one point in time. About 6 years to be exact, something I can't deny or regret. It certainly helped me jumpstart my dedication to events coverage. However, I was attracted to Canon when I began to see all the white lenses in highly inspiring and motivational events like the Olympics, presidential campaigns, and at local sports games in my hometown of San Francisco. It certainly made me very curious. Deep down inside, I wanted the speed, accuracy, and color renditions of the rapidly improving EF lens lineup. However, what really broke me in half with Nikon was when Canon released the ever so popular 5D classic. Everyone who's shot DSLRs for at least close to a decade know how much of an impact this particular model made when it was announced, and even bigger when all of the jaw dropping photos turned up. I can't really say that I switched, but when I bought my 5D with a 50mm f/1.4 my Nikon F4 never saw the light of day again after that. I had to sell it and settle for a 40D at one point but I bought the classic again when the Mark II got released. I kept loyal to the 5D series, and backed it up with a 1D mark III for shooting weddings eventually. When the 5D mark III came out I just had to do a double take and convince my boss to buy another one because the AF is just so buttery smooth with Canon lenses when shooting events. Then the 6D came out... I have to admit, I was disappointed. Canon gives us this war beast called the 5D mark III and puts a little innocent kitty cat next to it called the 6D. So I thought... Okay.... maybe my wife will like it. Maybe we can take it on vacations because it's smaller and lighter. Okay...it's so hard to defend against the D600 specs but we already have a lot of Canon gear...

After reading around in the Nikon forums, then going to the store to hold a D600 and try it out, I was disappointed in how it felt in my hands. Like Sporgon, the menus drove me nuts. I tested it in the store with a Nikkor 50mm 1.8 (which to be fair, feels better than Canon's 50mm 1.8 II BTW) Looking at the horrible LCD screen made me laugh, because it made realize that I was a film photographer that has become a chimper. But if I'm going to chimp, the LCD screen better be good. The slight green tint didn't bother me as much as I thought it would when reading about it. However, the image was cropped inside of the screen to make room for the settings... Wow. Even if that could be changed, it's really not a good idea to put that on a camera as default. Anyways, at that point, it really didn't matter to me what the Nikon images would look like on a computer screen anymore. I was holding a camera that an event shooter would have a bit more trouble using compared to a Canon system and even compared to the way my old F4 was. I'm used to my brother's D7000 layout, which I hate, and wish they changed it in future bodies. But nope, they brought almost all of it back. Also after that experience I have enough reason to believe that the live view/video mode is horrible on Nikon cameras in general. I'm also a cinematographer, and I am still facepalmed for Nikon for simple tasks like changing settings while in live view. I suppose they think everyone owns an entire set of AF-D lenses. This is an important feature with the most basic of functions that should have worked straight out of the box, seamlessly. The frustrating button placements and situations that caused me to menu dive constantly were enough to turn me off on just the camera alone. They should have kept it simple! These are vital operation constraints. Good photographers should be spending less time on the science of fiddling with controls, and more time on the art.

So I pre-ordered a 6D for my wife. I wasn't excited, of course. Being used to the 5D mark III, it was really hard to see that anything could come close. Now we have two Canon 6D bodies.... One for me, because my wife wouldn't let go of hers for me to really shoot all day with it. But the reason I have one now... The first impression. Holding it is NOT like holding a 60D. (which I've also owned more than one body of, previously) I think that's the common misconception by the general public who look at the specs and photos of the camera and say oh, it's a full frame 60D. It is not. It's definitely heavier, feels like I have a better grip on it, and the control layout seems to make slightly better sense. You will definitely notice that it is better built than a 60D from when you first pick it up. I have exactly one issue with it that the 60D might have a tiny advantage in. And that's the fact I can't program the SET button to go directly to white balance settings. I have a dedicated white balance button in the 5D mark III, why not the 6D? However, I said tiny because you can program the SET button for quick menu, and throw white balance into the quick menu. One whole button press behind, not that big of a deal unless you're shooting in a moving vehicle that passes different light temperature conditions in which you are required to shoot in at 5mph or faster. Seriously.

The AF is not comparable to the 5D mark III at all, and everyone is right in the regards of believing the very obvious truth that it is in a different league in that regard. But that's why people are going to buy the 6D, because not everyone needs the 5D mark III. Nor do they all shoot in death defying extreme weather. Back to AF, the 6D is no slouch. I can easily say it's AF is better than both the 5D mark II and 5D classic. In fact, I feel like it focuses faster than the D600 when I have a good lens attached to it like the 135mm F2/L or my colleague's 70-200mm f/2.8L II. Which is not a fair comparison of course, since I only used the 50mm 1.8 on the D600. I won't get in too deep with lens performance, but it does sort of make me feel like Nikon marketing is just throwing more points on the D600 to compensate for some of their lower performing Nikon lenses compared to Canon lens equivalents. Which of course, isn't true and I'm just a Nikon basher right? ~_^ Okay, so Nikon seems to have the edge on outer points for moving subjects. But in my 3-4 weeks of experience with the 6D, I can at least say that the outer points are very much usable in good light and a target with enough contrast, but it disappointed me for moving subjects. Note, this is the same disappointment I had for the outer points on the 5D mark II and 5D classic. Also note, I didn't know I had this disappointment until I became dependent on 1D mark III and 5D mark III outer point AF. So, if you're used to the old 5D bodies, or even the old 9 point system on the XXD bodies, you won't really feel a difference. The center point, however, is a miracle worker. With just a macbook pro lighting the master bedroom and not even facing the subject, I can lock focus and photograph my sleeping wife despite the fact I was forced to use ISO51200 to expose correctly at a hand holdable shutter speed. I'll have to test the same situation with a 5D mark III, but I know for a fact that even my 1D mark III couldn't do that or would hunt for a bit before it thought it could. The fact I'm able to lock focus on any shot that requires ISO51200 when my 1D mark III couldn't do it at it's highest ISO of ISO6400 changes the game a bit in that regard. I'm shooting a local wedding soon, and I'm confident enough to try the 6D as a backup body to the 5D mark III and see how it does in a very poorly lit church.

For high ISO performance, and sometimes, the way the images just looked at all ISOs... I was disappointed too, initially. I looked at some of my old 5D mark II RAW files, and they were obviously sharper when viewing the image full on. However, the softer images didn't bother me anymore after I saw how well it handled sharpening in Lightroom and unsharp mask in Photoshop. I loaded my 5D classic RAW files, and a lot of the ISO100 files looked cleaner somehow which I'm sure is because of the weak AA filter and bigger pixels. A friend of mine sent me a couple of D600 RAW files from one of his events, and they looked just as flat as my 6D RAW files. A lot of this is accurate towards what the general consensus is saying around the net with their tests. However, I don't care about the 100% crop tests because I don't deliver 100% crops to my clients. After editing all the files, I found that the 6D RAW files looked better than both 5Ds and still had more realism to human skin tone compared to the D600 RAWs. I can still praise the D600 in this regard, because despite the slight preference in skin tone, the D600 RAW files are quite good. However, I'm still in agreement with Sporgon on the fact I am not willing to trade Canon's weaknesses for Nikon's weaknesses. It's like trying to drive a ferrari with helicopter controls, it doesn't matter how fast your car is if you can't get it from point A to point B. Perhaps overboard with the metaphor, but you know what I mean. Canon warranty is better as well, but I won't get in too deep with that either. (Seems like I got pretty deep with everything else though, lol)

The bottom line is, you have to make sure you're buying the cameras from a photographer's perspective if you want it to do everything you need it to do. Like many say, the camera's eco system including lens selection and accessories is much more important, so narrowing this all down to just cameras will prevent anyone from making a truly open minded decision. Like I said earlier, I'd rather spend more time on the art of photography. I'm not a camera engineer, that's the camera maker's job. Specs, operation, and sometimes rumors, though they are important factors, are just a supplement to what it all comes down to and that's a good photograph. We're not supposed to be on the computer all day zooming in and shaking fists about dynamic range, we're supposed to be out taking photos. That's why I can easily recommend the 6D over the D600, because I know for a fact it does the job and doesn't give me long term issues that could slow down or harm my workflow in the field. But in conclusion.... All I can say is..... Just buy a 5D Mark III if you can afford it

- Ryan

Thanks for your informative thoughts. Well said from someone who shot Nikon, the 5D series and the 6D as well... I was once a Nikon user myself but didn't like the Nikon ergonomics, its lens system and from where I am, its after sales services is no way better than Canon....

you don´t have to quote everything....   

+1.  You don't have to quote everything. 

[Lord_Zeppelin]

I chose the 6D based on a few things, but mostly because I've always shot Canon. Despite only having 4 lenses and a flash and some other extraneous accessories, it would still be a hassle and relatively expensive (as an advanced hobbyist, semi-pro, whatever you want to call me) to chuck it all and go Nikon.

I actually have no issues with Nikon. They make good S___. It's the same argument, to me at least, as Apple vs. Microsoft, iPhone vs. Android, XBOX vs. PS3. I love tech, I am platform agnostic, and can/will change at any time. The D600 (and the D800 by extension) are pretty superb cameras, as is the Sony Alpha. I handled a D600, and it's nice, but the 6D just feels more solid. And it's probably just muscle memory, but the Nikon's "thinner" grips always feel slightly cramped to me vs. Canon, almost as if the edges are harder/sharper.

But what it all comes down to is that the differences are negligible - both cameras/systems have pros and cons. Just choose one, stick with it, and go shoot and have fun. Life is too short to agonize over the most minute detail.  For every 3 shots you miss with a 6D and it's "supposed AF weaknesses", the D600 will miss on sharpness on 3 photos that you will be upset about. I just want to shoot, use what I know, and be done with it, regardless of what badge is on it - because the photos matter more to me. I'm more concerned with making sure my knowledge base is solid, the mathematics and settings and framing and my own stability/grip - those things make infinitely more difference than a couple of MP or whatever else the spec-sheet elitists want to crow about with any given camera. 

[ecka]

My reasons:
1] EF 85mm f/1.2L II USM
2] MP-E 65mm f/2.8 1-5x Macro
3] TS-E 17mm f/4L
4] EF 8-15mm f/4L Fisheye USM
5] EF 40mm f/2.8 STM
6] better ergonomics
7] aperture control in LiveView
8] Magic Lantern
9] mRAW, sRAW
10] Nikon lenses are more expensive
11] Nikon's backward lens mount just feels wrong
12] I can use any Nikon lens on Canon body (via adapter), like 14-24/2.8G (which is an UWA lens, so manual focus is not a problem)

EDIT:
13] No green tint LCD!

[verysimplejason]

I'll buy the 6D if I can't afford the the 5D3.

[pdirestajr]

Ergonomics. I just don't like Nikon's digital bodies. There is much more to a camera than a sensor and a bunch of marketing features.

I'm not buying a 6D as I have no need for it, but I played with one recently and it felt really solid. Nikons feel like they are gonna break.

[Aglet]

I'd take the 6D over the D600 because it fits my hand better, I already use D800s, and I'd prefer a replacement for my FF Canon disappointment known as a 5D2.

I shifted from all Canon bodies to a mix of Nikon & Canon over a year ago because I could not push Canon files to the extent I needed to without running into their low ISO patterned noise issues.

My first Nikon was a D5100, cheap, great IQ, fits my hand well and was easy to get used to. Tilted sensor issue affects most of the 8 I've now tested but... they're under $400 now!  Best IQ/$ I've seen.

Next came a pair of D800/e bodies.  I love the ergonomics and compared to my 5D2 the raw files are fabulous for what I need. There's a button for nearly everything and once used to it it's very much a photographers' tool, programmable and adaptable enough for most jobs.  Requires 2 hands to operate more often than a Canon body.

I planned to sell one D800 and replace with cheaper D600 but, like the D7000, the ergonomics of the D600, for some reason, presses my irritation button, instantly.  Just plain hate the feel of the D600 and D7000!  It also was not worth the $1k savings to not have all the extra goodies I was starting to enjoy using on the D800.

I'm ready to toss my 5D2, it's raw files are too affected by low ISO pattern noise.
I had a quick feel of the 6D and like it.  It feels like a decent enough layout and likely performs better than my 5D2 but need to make my test shots before I know if swapping my 5D2 for a 6D is an actual upgrade.
Also, with rumors of improved sensor tech coming from Canon, I'd like to see a FF body that actually performs really well at low ISO. I can't say, today, if the 6D's low ISO has improved enough to be comparable to the $380 D5100's raw files.  6D's hi iso performance certainly looks better but that's not what I really need to augment my kit.
I want a FF Canon that performs much better than the 5D2 for low ISO IQ at similar resolution, nothing else is needed.
I will not buy another Canon body, however, until it is essentially free of low ISO fixed pattern noise like current Nikons are.

Gotta give it to Canon tho, they make a better user interface in every body they make, very intuitive.  Nikon's UI takes a lot more getting used to, often puzzling what some functions are until you learn them.
OTOH, Canon seems to re-arrange button layout on every model, so I often have to pull out a flashlight and look for a control in the dark.  Kinda wish they'd pick a layout and stick to it for a while.
One more major thing for me is that Canon's live-view works a heckuva lot better than Nikon's in low light. This is 5D2's amazing feature in comparison to even the latest Nikons.

Happy New Gear! 

[sdsr]

I’m very happy with my 5DII, but while that camera will seem to have superb low light/high ISO performance to anyone (like me) coming from any crop-sensor DSLR or lesser camera I’ve been interested by the superior low light performance of its successors.  A few weeks ago I rented a 5DIII, and was impressed by that, and last weekend I rented a 6D and D600 to see how they compared.  I had no intention of switching to Nikon, but I thought it might be fun to add a Nikon; the D600 was temptingly priced at the time, and a few Nikon lenses sound tempting (including the useful-sounding 28-300).  So, I wanted to like the Nikon, dust/oil issues notwithstanding.  But even if the D600 deals were still on, I wouldn’t want one because for my purposes there’s nothing about it that I prefer to the 6D or 5DIII.  (My purposes are evidently rather more limited than those of many here: I’m not a professional photographer, I don’t shoot sports/action, and I have no interest in video.  So there will be huge gaps in the comments that follow.) 

I didn’t perform any serious reviewer-style tests involving studio/lab conditions, charts, etc.  Rather, I wanted to see how they performed in conditions in which I actually use a camera, so I wandered around outside and inside, in low light and daylight, sometimes taking photos of the same things from the same place with each camera, at others just casually taking photos, always without a tripod.  One day was spent with my other half, who hasn’t been into photography since the film era, knows little about digital cameras (nothing about these two) and is thus somewhat of a neutral observer; we switched cameras from time to time.  I borrowed my father’s Nikon 50mm 1.8D and 85mm 1.8D, rented the Nikon 28-300 and used my own Canon 50mm 1.4, 85mm 1.8 and 70-300mm L.  Everything was shot RAW + JPEG and viewed on a very good 30” monitor.  Here are some observations, in no particular order (for all I know, of course, they only pertain to the precise bodies I rented).

1.    Some have sneered at the fact that while the D600’s viewfinder is 100%, the 6D’s is only 97% (or whatever it is).  What they don’t say is that the 6D’s is brighter and more accurate than the D600’s; the darker, slightly green hue on the Nikon’s makes everything look a bit drab, while what you see through the 6D has no coloration at all and is brighter.  I didn’t notice this difference until the other half started complaining loudly about it, wondering at one point why anyone would even want to photograph what they saw through this viewfinder in the first place. He took a surprisingly strong dislike to the Nikon which didn’t change in the course of the day (I kept defending it, but not its viewfinder…).
2.   I saw no evidence (on photos) of dust/oil on the D600’s sensor in “normal” photos (by which I mean that I didn’t deliberately take the sort of photo that would reveal them – no photos of the sky at f/16, for instance, though the sky appears in plenty of the photos I did take).  That may be because (1) Lensrentals clean the sensor before sending it out and I didn’t take enough photos to reintroduce dirt (2) the camera I rented never had the problem in the first place (3) the camera had been used enough for the problem to have stopped of its own accord (4) dust doesn’t reveal itself in the sort of photos I take (in which case I don’t care about the problem) or (5) some other reason.
3.   The D600 focused almost, but not quite, as well as the 6D in very low light.  It struggled a couple of times, but that’s all, and for all I know that was as much the fault of the lens as the camera.  Oddly, the only time it gave me a serious problem was outdoors in the middle of a cloudy day when there was enough light for the 85mm lens at 5.6 to trigger ISO 100: it completely failed to focus on a portion of a dark bronze statue.  The Canon focused on the same portion of the statue as fast as always.
4.   The greenish tint that others have noticed on the screen and which I’ve noticed through the viewfinder even ends up in RAW images, though it’s much subtler there.  It may in part explain why Canon’s images look warmer (in varying degrees) than Nikon’s when processed via Lightroom using the same settings (it makes some colours look a bit muddy).  Neither looks quite accurate, but I prefer Canon’s colours.
5.   The D600 consistently exposed brighter (sometimes to an annoying degree) than the 6D except in one particular lighting scenario at night where the reverse was true.  (My 5DII never does this.)  Of course, it’s easy enough to change exposure (on Canons, at least…  See below).
6.   Assuming it’s true that the D600 has superior dynamic range, as we’re constantly being told, this didn’t reveal itself in any comparisons I made among the photos I took.  In one dark photo, just for the heck of it, I brightened shadows as much as I could in lightroom, but the only difference I noticed was that there was a bit more noise in the Canon image than the Nikon equivalent – which I would have expected as it was darker in the first place.  (I seldom lighten shadows at all, and when I do it’s not by much, and the 6D’s images responded just fine.)   
7.   I generally prefer the photos taken with the Canon to those taken with the Nikon, but there’s not much in it.  Processed RAW files from both cameras are very impressive and the differences would likely strike most people as trivial (on smaller monitors they may be even less noticeable); I suspect that in a line-up most couldn’t tell which were taken with which camera.  Most differences could likely be removed via further tweaking with software.
8.   The 6D’s images in very low light/high ISO do indeed have a bit less noise than the D600.
9.   But even if the images looked exactly the same, I still wouldn’t want a D600 because I don’t like how the controls work (not the menus; they seem easy enough to figure out); my first DSLR was a Nikon D3100 and I was instantly reminded of one reason why I disliked using it: both make changing even some of the most basic setting so awkward it’s as though they’re trying to force you to stay in fully-automatic mode.  When I moved from Pentax to the 5DII I was able to figure just about everything out without looking at the manual; but it took me a rather long and frustrating time, including rereading the instructions more than once, to figure out something as elementary as setting the D600 to use center point focusing.   Why does making so many changes require simultaneously holding down one button with one hand while turning a wheel with the other?   Presumably one could get used to all this, and if the Nikon took better pictures than the Canon it would be worth the effort; but it doesn’t (at least, not for my purposes).
10.   Finally, I’m obviously not in a position to make sweeping pronouncements about Canon lenses vs Nikon lenses.  All I will note is that the photos I took with the Canon 85 1.8 are sharper (especially wide open) than those taken with the Nikon and have less chromatic aberration, that the two 50mm lenses are closer in daylight (I think the Canon is a bit sharper, but by a trivial degree), that the Nikon 50mm creates shocking amounts of coma at night (only a tiny area in the center seems free from it), that the two Canon primes seem mechanically a bit better than the two Nikons (for all I know their –G successors are better), and that the superiority of the 70-300L (both mechanically and in terms of image quality) to the Nikon 28-300 far exceeds the difference in price (and while 28-300 seems like a desirable range, it should be noted that much of the time it’s nowhere near 300, thanks to a rather excessive degree of focus breathing.)

That’s already more than enough, so I’ll stop!

[Aglet]

6.   Assuming it’s true that the D600 has superior dynamic range, as we’re constantly being told, this didn’t reveal itself in any comparisons I made among the photos I took.  In one dark photo, just for the heck of it, I brightened shadows as much as I could in lightroom, but the only difference I noticed was that there was a bit more noise in the Canon image than the Canon equivalent – which I would have expected as it was darker in the first place.  (I seldom lighten shadows at all, and when I do it’s not by much, and the 6D’s images responded just fine.)   ..
That’s already more than enough, so I’ll stop!

Thanks for that bit.  That's what I'll be testing when I can spend some time w the 6D as I often take shots where I will be pushing shadows a fair bit.  good to know I may not be wasting my time.

[RustyTheGeek]

verysimplejason - ROFL!     You beat me to it!  Gawd, I was thinking the exact same thing and I had to restrain myself from quoting your quote of the other quotes that I didn't need to quote!!  Ahh, ha ha ha ha!!!  You are so bad!  I Love it!