I love Alien and Aliens but I also very much enjoy Alien 3, Alien Resurrection, AVP, and Prometheus. I also enjoy all three Predator films but for me they are on the Alien Resurrection level as they are fun enjoyable movies but just that.
Alien 3 felt more like Alien which was great. With a movie that had major studio interference it turned out to be good IMO. Shame that the director disowned it.
Alien Resurrection to me is 100% stupid fun. I enjoy the hell out of it. Sure, the newborn was stupid but it worked with the over the top tone. I hate it when people compare it to Jaws the Revenge as that movie was just plain boring. You can tell that the cast were having a blast making it. Stupid movie, yes. Fun movie, yes.
AVP is my least favorite but I still enjoy it. I think the AVP franchise has its own continuity.
I love Prometheus but the characters were stupid in it. I love learning more about the species of the Space Jocky but I know it disspointed many with different visions on their species. The film had great special effects and cinematography.