It's always a toss-up between the first and second, isn't it. I'd say Aliens is my favorite, but it's a hair's breadth of difference. My actual controversial opinion is that *all* of the Alien movies are good (except AVP 2).
I actually like Escape From L.A. a lot. But the best ones are, of course, The Thing, Halloween, Big Trouble in Little China, Assault on Precinct 13, Escape From New York, etc.