Animal House, definitely. I have to agree with KB here in that I don't see what's so fascinating about Annie Hall. Animal House may not be Best Picture material, nor is it going to win Best Visual Effects or anything, and it didn't "revolutionize the film industry", but its a classic! Damn near every school related comedy is compared to it and none of them match up.
Otter: Let me give you a hint. She's got a couple of major-league yabbos.
Boon: Beverly!
Otter: No. But you're getting warmer. Here's another: "Oh God, Oh God, OH GOD!"
Boon: Marlene! Don't tell me you're gonna pork Marlene Desmond!
Otter: Pork?
Boon: You're gonna hump her brains out, aren't you?
Otter: Boon, I anticipate a deeply religious experience.
The horse scene? The ladder scene? Etc etc etc.
To paraphrase: See if you can guess what I'm voting for now...
Animal House.