I have a lot of favorite movies, it would be hard to name my number one favorite.
But, one of my top movies would have to be Alien/Aliens.
I'm in love with those Xenomorphs.
In fact I have two Xenomorph action figures; a 6 inch Revoltech Alien and a 18 inch NECA Alien.
I love them both.
But yeah, I love the artist that designed Alien (H.R.Giger), and the movies are quite enjoyable. The first movie is great for that creepy-scary feeling, and the second one is great for action-adventure.
Also if we're talking about horror movies, The Thing is in my top list as well.
It may be an old movie, but they did a lot of things right in that movie. Even now some scenes just creep me out, which is amazing since they didn't even start using computer graphics back then, just all man-made handy-work.
I can safely say that The Thing scares me more than most modern horror movies, which are all just hack-n-slash, let's-see-how-many-ways-we-can-kill-these-teenagers type movies.
Can't say much about The Thing remake/prequel since I haven't seen much of it, but I'm not expecting very much. The Thing is just one of those movies where it would be very difficult to re-create the same feeling of the first one.