If you could only buy one of these Canon super tele lenses :

200-400mm f/4 L IS Ext 1.4x
400mm f/2.8 L IS II
500mm f/4 L IS II
600mm f/4 L IS II

which would you choose for photographing wildlife?

I have worked for some years using the Canon 70-200mm f/2.8 L IS; the Canon 100-400mm f/4.5-5.6 L IS
and the Sigma 150-500mm f/5-6.3 APO DG OS as well as a 1.4x Extender. The zoom lenses have proved mighty
handy when animals moved close up to the hides / safari vehicles. The extender has had its uses but with some
lenses/bodies there are autofocus issues and potentially hazardous moments when fitting/removing it in dusty or
damp environments.

I realise my question is a bit hypothetical as three of the above lenses haven't been released yet but I want to
start canvassing opinions now.