I'm not talking about your -favorite- movie. I'm talking about the movie that you consider the absolute best ever. For example: I consider There Will Be Blood to be the best overall, although my favorite is The Matrix.
Uhhhhh I haven't really ever thought about this, but I think Black Swan was as good a movie I've seen in a long time. And it has held up after multiple viewings. So: Black Swan
Best film of all time? Lawrence of Arabia. Gone with the Wind. I'm Gonna Git You Sucka. "My b**** better have my money/Through rain, sleet, or snow/My ho better have my money/Not half, not some, but all my cash/'Cause if she don't,/I'm gonna put my foot in her a$$."
Lots of candidates.. Jaws Silence of the Lambs Young Frankenstein Forrest Gump Star Wars Avengers The Graduate I think you would have better luck just looking for the best of the cream of the crop.. there are way too many great great movies.
I haven't seen 90% of the old classics, but shawshank redemption is so, so good, especially compared to the book. I never get tired of that movie. tied with team america: world police.
The number of ways that a movie can be great is so great, it seems a little ridiculous to put them all in one big bucket and ask which is the best of them all. Some are great for great acting, others for writing, others for cinematography. There's no way to fairly compare across such breadth. With that caveat, I'll go with Freddie Got Fingered.