I've been borrowing the 5D3 recently and ended up selling my Nikon D700.
Here's my beef. I DO NOT like Canon ergonomics. The button layouts to me make no sense. I have to run around in menus to get to things, and it's just a difficult thing to do. And this from owning a 5D2 for almost a year.
My Main camera has been the Nikon D700. It's autofocus and continuous focus is miles ahead of the 5D2. I love the placements of the buttons. Love Nikon's menus. So why did I sell it?
My Canon's White balance accuracy and overall colors just flat out blows away the D3 sensor in the D700. Colors have much more pop and much more accurate white balance. It would take me forever to post process Nikon files for correct skin tones. Post processing Canon CR2 raw files are a cinch.
Just thought I'd share. I really miss the Nikon ergonomics. When it comes to ease of use, the menu, the customization, Canon is really far behind Nikon IMO. But for sheer picture quality if you expose properly (ie, dynamic range in shadows not pushed), I find the Canon tones are much more to my liking.
All in all, I am more inspired by seeing the final pictures from my Canon, than I did with my Nikon. That to me was the deciding factor.
You've just nailed a major reason why I made the move to Canon from Nikon a few months ago! I used a D700, and the switched it to a D600 (i need the video function), I didn't get on with the AF/erganomics of the D600, so I returned it. This left me realistically with the only option being a D800. I downloaded a number of RAW files, and while the DR and detail was amazing, I found the colours and tone straight from camera, to be worse than the D600. Also, as much as 36 mp is obviously an advantage in some situations, the file sizes (even compressed) were still very large.
I was able to borrow a 5Dmkiii and a couple of lenses from my works advertising dept for a weekend, and after a couple of days I was sold! I couldn't believe how finished the RAW files are straight from camera, and how little processing they need. Nikon certainly have the edge when it comes to shadow recovery, but for what I shoot this can be overcome with bracketing if needed. Also, I found the Canon tends to meter darker, which confused me at first.
As far as the erganomics, I found myself adjusting quite easily, and actually prefer the way the Canon feels now ( I still use Nikon daily in work, so I've directly compared both!).
I got a lot of stick from fellow Nikon shooters when I made the switch, but the way I see it is a camera is a tool, and I use the one that suits me best. If Nikon had made a D800
with the option for Small and Medium raw files, and "Canon" WB and colours then I would have probably stayed with them. But as I said Canon simply make the camera that I need at the moment.