I thought the whole atmosphere processor shenanigans in Aliens were great, personally. Maximum tension there, and I like how some of the marines disobey Gorman's orders (was it Hicks who pulled a shotgun from his backpack?). I hold Aliens (Director's Cut only) as the equal to Alien but not for the same reason. The latter is the ultimate horror film in my eyes while the former is the ultimate action film. The best part being that they both share the most badass heroine in cinema. The other two films are forgettable.