The recently reignited debate about sensors performance and Nikon's superiority have led me to post this to make the canon users feel better!
If you shoot sports/wildlife you might want to take consecutive shots, FPS is important.
If you shoot raw, buffer may be an issue .
Here is 3 seconds of action
3 seconds of action
d800 : 12 shots
d7100: 14 shots(at best, the buffer is terrible)
d600 : 16 shots
6d : 14 shots (AF might be an issue)
5dIII: 18 shots
7d : 24 shots
1d4 : 30 shots (if you want to buy, it must be second hand)
d4 : 30 shots (high price)
1dx : 36 shots (high price )
The only affordable nikon ( so excluding 5-6K$ cameras like d4) that has a decent enough frame rate and buffer IMO is the d600. Well the d600 lacks the AF system that the d7100 and d800 have..., it's autofocus is far inferior to those....
In the canon segment, I think the 7d, 5dIII and 1d4 are all wonderful alternatives (the 70d should have 16 shot buffer, so you might get 19-21 shots in 3 seconds).
The 5d3 focus system is better than that of the d600, the 1d4 focus system is also better.
I am not sure if the 7d/70d focus system trumps the d600.
All in all you have a lot more choice for sports/wildlife on the canon side!