Best Sci-fi / Horror Movies

This is a tough one, because both the first and second are excellent. I would learn more toward the second because it had multiple aliens, the queen and delved more into how these creatures exist.

And I do agree that The Thing should keep its 3rd spot. Another great film.

The best alien yet, Sigourney Weaver gives a chilling performance, she is more hardcore now, because she has already encountered an alien so she knows what to do in this one, She was nominated for Best Actress in a Leading Role she should've won the Oscar!

How is this not in the top five?