I think Alien, Alien Isolation, Aliens and perhaps Alien 3(maybe, on fence about it even I like it) work well as a basic core that should be canon, anything added to that could just be what ifs or parodies (Alien rez), well atleast if they are messing with the lore. Prometheus and Covenant don't belong in my opinion, not only aesthetically, but it adds stuff that just contradicts stuff and even reduces the alien and the world building in my opinion.