I would go for: 2001: A Space Odyssey / Inception / Good Will Hunting / Fight Club / 12 Angry Men I like things that are pretty easily watchable but also have something a little deeper going on behind the surface if you want to dig in a bit. It was hard paring out Pulp Fiction and The Shawshank Redemption. I haven't really watched a lot of the classic movies though because I usually feel they're too slow. They feel faster when watching with a group though, so I try to do that every now and then.
Those are all great films and they are all pretty different from one another. My favorite on your list is 12 Angry Men. We used to have a Hubski Film Club where we would pick a topic and watch a film or two in that genre/topic. We decided to pick the Director Sidney Lumet's first and last film to watch. They were quite different. His first was 12 Angry Men -such a wonderful film. He turns his limitations in to virtues. I think I started sweating during the film because of how convincingly he made it appear that it was scorching hot. -Wonderful work. We ought to resurrect the Hubski Film Club. I know kleinbl00 has a scifi club going. b_b, you were in on the film club. Those were good times.
Right now we've got an Anime Club. We're gonna have a fiction club and a non-fiction club. I'm firmly of the opinion that there shouldn't be more than one -club at any given time because fatigue sets in. For the next two weeks, it's Anime Club. Watch Madoka Magica. Do it. It's that good.