Alien has been my favourite film as in, as long as i can remember.
It wasn't yet when i was a teenager, as i was too young to really appreciate it. I do remember seeing a good part of the movie as i sneaked behind the couch of my parents watching the movie. i guess they were so into the tension of the movie that they didnt notice i was enjoying the tension too.
weird, really, as i was absolutely frightened to death by ET. i remember that scene in the bushes with the finger and it scared me to the bone. I yelled and cried like a pup. Yet somehow with Alien, I was absolutely mesmerised and stunned by the awesomeness.
My parents noticed i grasped for breath i guess when the alien went for lambert. i never did see the chestbursting scene back then i'm sure that would have had some negative impact.
Movie always stayed with me. All of them, really. Obviously Alien tops it, and Aliens is a good second. I dont mind 3 and Resurection, really.
AVP was a letdown. Messy. It was fun from a fun point of view, not in a franchise-abusing way, and i was less enjoyed by Weyland and Bishop's portrayal. Requiem was absolutely tasteless and shamefull. I immediately grew a deep-filled resentment against the Strauss failures.
Anyway, my favourite Alien movie aside the alien universe would be I guess Predator and Independance day. (the one with Will Smith in it, not the new one). Also 'Sphere' i really enjoyed.
I felt goosebumps during Independence Day when first hearing the signal. Must say though i never felt any 'tension' during the movie. It never had a real horror feel to it to be honest - not that it intended that i think. It could have made a good one had they implemented horror better in it.
ah and really enjoye "The Body Snatchers" too. a lot.
but as for the franchise movies:
1) Alien
2) Aliens
3) Alien3
4) Alien: Resurrection
5) Prometheus