Regards the 7Dii it all depends on what your main area of photography is
http://www.clarkvision.com/reviews/evaluation-canon-7dii/index.html
Blanket statements like 'the D800 is a better camera without saying what you use it for is meaningless.
I never said that the D800 is a better camera than the 7DmkII. I said the 7DmkII was a sign [that Canon was unwilling or unable to execute a better sensor subsystem at the current time] and therefore it would be a good time to switch if he was so inclined. The 7DmkII is by far the best low light, crop sensor action camera on the market. Nikon has nothing to compete in that niche which is inexcusable (former D300 shooter here). But the original poster is looking at Full Frame.
What I will say, is that the D810, in my opinion, is the best
general purpose DSLR on the market. (The D750 has some attributes that elevate it above the D810 as a general purpose camera, but shooting in crop modes leave you with very little image to work with.) The D810 sets the standard on the landscape side for resolution, DR and low noise shadows at the current time and is fast enough for most action use, especially shooting in 1.2x or 1.5x crop mode. I shoot sports with the D810 regularly and find it not only faster than the D7100, but more than sufficient for most sports and action needs. It certainly would not be the go to camera for super high speed action where you really need 8-12fps though. But those instances are exceedingly rare!
I keep going back to this
John Shaw quote on the D800 (much slower operation than the D810 in every way):
“Can the Nikon D800 be used for wildlife photography?” Well, why not? Here are two full frame images taken last week during a short stop I made at Bosque del Apache. Both images: D800E, Nikon 600mm, ISO400, early morning light. FYI, I don’t have the extra battery pack for the camera so the motor drive rate is 4 frames/second. Anyone else remember when 4 frames/second would have been considered pretty amazing? Remember winding film with your thumb?"