Oh, you're including Prometheus in this? Interesting. Okay, I'll give it a shot.
1. Alien: Just a classic. The pacing is perfect. Although some of the effects are VERY low tech, the movie still looks very real (other than one very brief scene).
2. Aliens: A much different movie than the original, but still very much a classic.
3. Prometheus: I thought it was cool, even if it did have some inconsistencies and holes. Knowing that it is part of a series of films, it is hard to rate because it may seem better or worse once in context with the other films after they are done. It's hard to see it passing Aliens, but it may move up a bit closer (there is a big gap between #2 and #3 on this list), and it could fall below A3 as well.
4. A3: Close call. I almost put it ahead of Prometheus. There were some problems with it, but it was decent.
5. AvP: Ranks FAR below the rest on the list. This was just a series of missed opportunities. It was still okay, but should have been so much better. It probably would have been if it didn't feel like a video game.
6. Resurrection: Falling farther down the list...it had some really interesting moments. Unfortunately, it had too many head-scratchers as well.
7. AvPR: Again, SHOULD have been much better than it was. Ever since the Dark Horse AvP comics series in the '90s, Alien and Predator fans longed for this to be done onscreen. The sheer terror factor of these things being unleashed on earth should have taken this movie over the top. But it was so poorly done, and so much Alient "cannon" was disregarded that it just became painful to watch rather than the unbridled awesome it had the potential to be.