Hmmmm.... spot the odd one out. I guess The Sixth Sense is included cos it was THE movie that everyone talked about that year, but I don't think it's better than American Beauty, let alone the other two nominees! Plus, if you guess the twist, the film isn't half as good.
I always find it tricky when it comes to Citizen Kane. It almost always tops critics' and directors' list of best films ever made. Orson Welles practically invented cinematic directing due to the use of completely novel techniques like filming Kane from below to emphasise his power and have been aped ever since. However, as a movie to watch, I didn't really enjoy it that much. It's one of those films you feel you're supposed to like, but it felt a little too like a film masterclass for me.
2001 on the other hand is a great movie but with one huge drawback. The ending doesn't quite do the rest of the film justice. It's amazing to think that the first word isn't spoken until 30 minuts and the effects of the guy jogging round the station or the space-hostess walking vertically are still incredible. It's also brought many things into our culture like the black monolith or HAL, which is the hallmark of a classic.
So, you won't be surprised to hear that I'm going with 2001: A Space Odyssey.