I'm a religious Nolan fan, so I went with Memento. Tough call though with Rear Window and Seven Samurai in the race-
Following is Nolan's best. Had that been up against Rear Window, I might have had to vote for it...
It's at least the one with the best bang for the buck, it cost only 6000$ to make.
Regarding his best film, I am torn between "The Prestige" and "Batman begins".
I mean Following was great, Memento was great, Insomnia was good, but Prestige and BB were incredible.