Kind of depends on which one I have most recently watched, Hadn't seen Memento in years, and I watched it again this past weekend. Really excellent. But for now, I will say The Prestige. For a while I was on a big Inception kick, so that slides into the #1 slot sometimes for me, as well!
__________________
“Film can't just be a long line of bliss. There's something we all like about the human struggle.” ― David Lynch