I'd Rather She Not Come Back for Alien 5
I think Sigourney Weaver is a tremendous actress and the Alien movies are my favorite movies but I would prefer if she doesn't return to the franchise. I feel that Alien 3 has aged much better than people give it credit for(particularly because of the Assembly Cut) and makes a definitive conclusion to Ripley's story (I don't consider A:R as part of the franchise). As far as I'm concerned, Ripley's story ended with Alien 3.
I think Neill Blomkamp's biggest strength as a filmmaker is that he has a great eye for detail and is a very good world-builder. Alien 5 is an exciting opportunity to expand the universe in a way 3 and 4 didn't. I think it's a franchise that would benefit from having new characters instead of relying on Ripley to tie everything together.