I voted Alien 3 (Flamers can piss off right now).
I just liked the idea, it was differently set up than Alien, but had the same sort of dynamic. I liked the Dog Alien design, its just a shame that they screwed Giger around during this one.
My fave character from any Alien movie was Morse incidentally. He was a coward, and an annoying loudmouth, but I always thought he did it in a funny way. Especially the scene where he is laughing with his friend with the bandaged head, then his friend gets headbitten. Also his constant and obvious attempts to piss off the other inmates.
"Hey guys... My door ain't workin' I think we better re-think this thing!"