Everyone has different needs, so here's my $0.02 as I'm sure there's others who can relate.
Let's address the never ending quest for better and better bodies with an age old fact -- LENSES far outweigh BODIES when it comes to results. They are a bigger part of the equation. No crappy kit lens can ever get the same portrait look that my 70-200 2.8 II can. Doesn't matter if I have the best and newest bodies on the market.
Canon, as we all know and even Nikon and Sony people can mostly admit, has the best glass. Sure, they can get edged out here and there on sharpness, or maybe speed or some other factor. But, when you combine speed, IQ, price, and all factors, Canon is a clear winner. Canon 24-70 2.8 II is street pricing from authorized dealers in the $1,500 range. This lens beats up the Sony and Nikon equivalents easily...just one example. The 16-35 is another example, both he F4 and 2.8...The 70-200 2.8 II, Nikon has finally matched it, but for $1,000 more!!!!
Now, Canon is not the most cutting edge on bodies. Most can admit that here. They'll justify it 100 different ways, some legit, some are a stretch. But the fact is, you can get better bodies elsewhere. However, in the end, when you take a great lens and a decent body - you get good results. The competition has great bodies and decent glass that gets good results.
Ok, all that said -- this is what *I* do...
I own a set of 2.8 L glass and some good primes. Right now, I run a 6D. That's it.
Here's why.
The 6D is a very high value body. It accomplishes what I need for about 95% of my uses. I'm not a professional photographer. 6D can give amazing portraits, landscapes, macro, even some sports or action if you can time with your finger. For my day to day, week to week regular photography - it is more than what most people need.
Remember, there was a time when 20mp was considered amazing super high resolution....
I'm not here to promote the 6D. My point is, make an accurate assessment of what your real, day to day NEEDS are. That's what I did. And for my needs, the 6D is pretty darn good. It will serve me well until Canon offers up a better value full frame like the D850 or A7R3.
In assessing my needs, I asked myself the following --
How often do I really, truly need 10-14fps?
How often do I really, truly need 50mp?
How often do I shoot landscape with the intent to print wall sized?
How often do I really, truly need an AF system that can track a football player going down field?
How often do I get paid to shoot an event where I need dual slots to avoid a disaster if memory card fails? (I'm not a pro, but will pick up some small work here and there)
In MY uses....that is less than 5-6 times a year, if that. Again, scenarios where the above features are a MUST to get the images. Not scenarios where it would be nice to have, but scenarios where it's needed. Very few.
So what I do is, I rent the 5DSR, 1DX2 or more often the 7D2, or 5D4 depending on what I need for the occasion. Renting is not cheap, but it is far, far, far cheaper than buying any one of these cameras and eating their depreciation. These are expensive bodies which are updated by Canon every three years.
At 20mp, I can capture stunning landscapes that no one, except for maybe some rich person who has an 8K monitor, can even view at full resolution. So unless I'm going to print huge which is very rare for me and I bet rare for most people, I don't need a 5DS. I also don't need to blaze away at 14fps. My most commonly needed camera is a 5D4. This is because it has better AF for moving people like a wedding (not sports), dual slots, and more speed than the 6D for events. I'll rent this body for 3 day or 5...doesn't cost much and I get results when I need it.
The last higher dollar Canon I had was the 5D3. Great body and for its time a good value compared to the competition. I sold it a little before the 5D4 came out. My "cost of ownership" was approx $700 for 3 years. That's a little over $230 per year and that's pretty cheap. I didn't do the same thing again with the 5D4, because I don't feel resale will be anywhere as good sometime in 2019-2020 given what the competition is putting out and I don't want to deal with the process.
Instead, I just run a cheap 6D - I get quality that 99% of people cannot appreciate anyway and I get out of the never ending upgrade cycle that is costly.
People who buy and keep bodies have to be satisfied with them for a long time (6-7 years or more), otherwise that's a lot of cash to put into something that depreciates so quickly. Lenses hold value more, aren't updated as often, and again, are the most important factor in IQ and achieving the look you want. So it is better to own glass, and rent bodies, than own bodies, and rent glass in my opinion.
Sure, the Sony A7R3 is a killer. But their lenses are not that great. It isn't worth spending that much money on that body for me. In 2 years or less, the A7R4 will be out rendering this thing ancient and depreciating it more. Sony glass isn't terrible, but it costs considerably more than Canon and at the very best, in some examples, only equals it. The grass is not greener on the other side. Canon might be a bit conservative, perhaps even stingy with specs, but in the end - the IQ is at least as good, if not better. Despite the "worse" sensor, and less specs in bodies. It's the final result that matters.
If you're not made of money to be upgrading bodies constantly, or not a full time working pro -- I think either owning one body and being happy with it, or using the rental approach as-needed like I do does better for costs and results long term.
I know that I do not exceed even $900 in rentals per year. Not even close. That's $1,800 every 2 years at the worst which is an overestimate. Still less than buying a semi-pro body new and owning. I get to then use specialized cameras that dominate for the intended purpose.
If you buy and sell, the cost comes down, but - the problem with Canon is, do you buy and sell off a sports camera, a high res body and others every cycle? If you add up the loss per camera - it becomes a lot. The cost of ownership goes up quite a bit. Nikon D850 is a real first in a sense, in that their users will now have a camera that covers a lot of other bodies all in one. It's a high rez landscape and portrait camera, an event camera, a sports camera, wildlife. Not much it can't do. That's a high value and worth the $3,300 asking price. It reminds me of the leap the 5D3 was in its time.
So I'm no mirrorless fanboy -- but I look forward to the day that I can get mirrorless advantages with my EF lenses in FF with a Canon first party AF camera.
