I've got to give the edge to SKYFALL. In terms of pure spectacle, THE DARK KNIGHT RISES wins hands down, as its just a bigger, more expansive movie. In terms of a cohesive, watchable piece of art with good exploration of its themes and concepts and good execution from actors and the rest of the filmmaking team, SKYFALL wins hands down. The acting is better and more nuanced, the writing is better, the humor is better, the pacing is better, the action is more believeable and visceral, and I think there’s no contest in terms of cinematography.
I do think it’s somewhat amusing that while the influences in his action score is obvious, Thomas Newman kind of does Hans Zimmer better than Hans Zimmer. That man can flat score fireworks (See MEET JOE BLACK).
As far as Sam Mendes making the Bond film Nolan would…I don’t think so. I think evidenced by his Batman films and INCEPTION, Nolan's Bond film would likely be much, much larger in scale. Mendes made a very personal, almost subtle, Bond film. He and Nolan have almost opposite approaches, save for a desire to ground things a bit, which the entire Bond reboot has aimed for.
As far as similarities to Nolan's Batfilms go, in particular THE DARK KNIGHT...they were pretty basic and minimal, really limited to one key section of the film, and I think Mendes came out ahead there comparitively. SKYFALL is just a more consistent film than THE DARK KNIGHT RISES or THE DARK KNIGHT (though TDK has enough high points that I wouldn't want to begin deciding which is the better film between SKYFALL and TDK).