Overall they are all good camera, at the end of the day it mostly comes down to how you can use them and how everything is setup, the 6D for wildlife I had the most dramas with as its really not designed for it, with FPS + AF, making life really hard, useless at times, unless the subject is somewhat still...if you can get a 1Dx its far better of a camera and features the benefits from all of them really, it takes a lot of the hard work and frustration you could say away and makes it easy when/if you changed over from a 7D or similar, its highly noticeable and the hit rate is night and day difference over the others from my experience. Don't get me wrong they are all great bodies that can achieve the results, but to save the stress just grab a 1Dx makes life easier, that being said the 7D II setup right can be a beast but if your in the market go 1Dx.