What's your budget?
+1 It really depends on how much you want to spend.
You listed these criteria:
Better autofocus 1DX, 5D3, 7D
Handling 1DX, 5D3, 6D, 7D, 60D
Low light performance 1DX, 6D, 5D3
Large, bright viewfinder 1DX, 5D3, 6D, 7D, 60D
Versatile (landscape, portrait, minimal action) 6D, 60D
Limited size and weight 6D, 60D, SL1, 650D
So, depending on how you weigh these factors, your choice could be anything from a 1DX to a SL1. The 6D might be best all-around option as it makes the list on all factors except "better autofocus" and its decent there, but not great. Fine for everything but a lot of fast moving sports.