I realize this is an old thread but I am a recent visitor to these forums and loved this thread. This is a topic near and dear to my heart. I watch these things while modelling. I can't narrow it down to three films so I have to cheat.
My top 3:
A - Alien - I classify this as a Horror film that happens to be set in space. Hard to think of a more shocking scene in film than the alien "birth". Linda Blair with a crucifix? The Crying Game "revalation"?
B - John Carpenter's The Thing - I don't feel this is a remake of the original Thing at all. Carpenter's Thing more closely follows the original novella written by John W. Campbell, Jr. in 1938 and recognized by The Science Fiction Writer's of America as one of the finest science fiction novellas ever written.
C - Blade Runner - What a vision of LA! Rutger Hauer was great. Sean Young was beautiful and the soundtrack by Vangelis was extraordinary.
My 3 Runner-ups:
A - Aliens - When I first saw this on the big screen in THX I thought it was the most exhilarating movie I had ever seen. Flight Lt. E. Ripley - toughest character ever?
B - Terminator 2 - I really agonized over this choice. Terminator or T2. In the end, I think I was swayed by a tougher Sarah Conner and a very unique and well-played villain.
C - Star Trek II - Ricardo Montalban...nuff said.
Honorable mention:
A - Terminator - Best SF line ever. "You're terminated ..."
B - Predator - No, I don't really like Arnold this much. These picks just worked out this way.
C - Matrix 2 - Best freeway scene ever. Best latex ever.
Golden Oldies:
A - Invasion of the Body Snatchers (Original) - but I did think the Donald Sutherland version was just as good. And with a cameo by the original dude, Kevin McCarthy.
B - Forbidden Planet - The Id has bailed me out of many a Scrabble game. Best Toga ever. I'm glad I saw this years before the Airplane or Naked gun movies so I could take Leslie Nielson seriously.
C - It! The Terror from Beyond Space - OK, maybe this should have been on my guilty pleasures but I like it and it was really the forerunner of Alien.
Guilty Pleasures:
A - The Blob - Scared me witless as a kid and I still don't eat Jell-o.
B - Reptilicus - Back when there were only three channels on TV there was this thing called the Million Dollar Movie. They played the same movie every day for a week. You guessed it. I may be the world's only Reptilicus expert.
Tony