I have been comparing the specification of the Canon EF 500mm f4 L IS II USM Lens v Nikon 500mm f4 ED VR AF-S Nikkor Lens please see table below:-

The important numbers listed above for the wildlife photographer is the minimum focus distance which Canon wins 3.7m compared to Nikon’s 4m, also the weight of the lens is of importance again Canon wins at 3190g apposed to Nikon’s 3800g.

Nikon does win on cost by quite a long way, but if you want the best lens on paper then Canon wins on minimum focus, weight and has more lens elements.