It actually depends.
If voting for the scariest and most thrilling movie - then Alien. If for pure action slaughterhouse - then Aliens. Third one I disliked because of the love scenes. Fourth one .. I don't want to talk about it.
Voted for the first one because it's scary(est), because for that time it's unbelievably original and well made. Still from time to time I watch it over and over again. Never getting bored and always it's like watching it for first time ...
