Huh?!? You would put aliens over alien I terms of quality? And depending on your idea of quality Prometheus could well be top, of the series it's the most visually stunning
...my idea of quality? Oh hello there, mister-i-make-silly-assumptions-about-other-people.
I felt Aliens was more tense and slightly more paranoid than the first film... and it just has better dialogue and character work.. the 80's action movie vibes may put some off.. but please do consider that these films are essentially Bmovie stories with Aclass moviemaking. They werent made to please pretentious twats.
Prometheus just isnt as tight in it's storytelling as Aliens or Alien.