#1: Alien is what I consider to be one of those rare, perfect movies. Yes it's slow, but it's not an action flick. It's a horror movie with very real characters, high tension and the srangest, scariest monster in any film.
#2: Aliens. An awesome action flick with plenty of tension and great characters. Although I prefer Alien over this one, I watch this one more than any of them.
#3: Alien 3 (the assembly cut). When I saw this cut for the first time I was floored by how much better the movie became and in my opinion it needed it. It's now VERY good.
#4: Alien: Resurrection. I hate this movie. What a stark contrast to the original. In this movie the aliens have effectively been reduced to comic relief. There's no tension whatsoever. Who cares if THIS main cast is killed off anyway? Sure there are funny moments between them but when you don't really care who gets picked off next, well, it's not a good sign. Plus the new alien design introduced is crap. It goes from a bio-mechanical being to a fleshy, always-drenched-in-slime raptor... thing.