If your wife is getting more serious about wedding and portraiture photography then the 6D is the better choice.
Sorry to be the bearer of bad news, but serious wedding and 6d/5d2 af system doesn't square. You can use it as a 2nd or backup body, but for anything mission-critical that moves this is not the camera you can rely upon. Think of the couple walking down the church alley, your af tracking fails and you have to say "Well, you know, I saved $1000, could you please repeat it?".
There are plenty of excellent wedding photographers using the 6D as their primary camera. Dustin Abbott, who often posts here is one. A local photographer, well regarded as the best in the town I live, uses a 6D as primary and 5D2 for his second shooter and doesn't have any AF issues with these bodies.
I'll be the first to admit the 6D's AF is not nearly as good as the 5D3 or 1Dx, but it's not bad either. Unless you are shooting lots of sports or fast paced wildlife (BIF), the 6D's AF is probably good enough for most uses including weddings.
No offense but I own the 6D, 5D3 and 60D (not to mention many other Canon bodies) and I am fully confident in the 6D autofocus. In fact, until a firmware update fixed the 5D3 low light AF issues, the 6D stomped it with low light AF. Don't run away from the 6D because some folks think it has flaws compared to the 5D3.
As for the OP question about 'best all-around body', I also would tend to agree with candc, the 70D is likely the best all around for your needs. Better video, speed for sports, etc. A FF sensor (6D) will open up a whole world of creativity but you can still create great images with an APS-C camera and that's the format you are already accustomed to anyway. Get a 6D ASAP later but get the 70D first and get busy making money to pay for other things. Buy most of your lenses in EF type so you can use them on the FF camera in the future.
I think we are generally in agreement. Maybe my wording came across more negative about the 6D's AF than I intended? I own a 6D and have borrowed or rented 5D3 's and a 70D with enough use I think I understand each bodies strengths and limitations.
For most photography not involving fast moving sports or BIF the 6D's AF is good to very good, excellent AF accuracy and precision. Certainly a good option for weddings and events as well as landscapes, portraits and street shooting. The 6D's AF does struggle in AI Servo when compared with the 5D3 and to some degree the 70D in my opinion, partially due to the limited number of AF points. But, AI Servo is a very small percentage of what I shoot, so the 6D is a terrific body for my use.
I agree that the 70D would be the best "all around" photo/video body to upgrade from a Rebel for the OP's stated purposes.
« Last Edit: May 27, 2014, 07:42:32 PM by bholliman »
Bodies: 6D, EOS-M (22/2 and 18-55)
Lenses: Rokinon 14mm 2.8, 35mm 2.0 IS, 85mm 1.8, 100mm 2.8L IS Macro, 135mm 2.0L, 24-70mm 2.8L II, 70-200mm 2.8L IS II, Extenders: EF 1.4xIII, EF 2xIII ; Flash: ST-E3-RT, 600EX-RT (x3)