Ok, assuming all films including (shudder) AVP and AVP:Requiem are considered canon, does the timeline go something like this (and please note, I still haven't been able to bear the thought of watching AVP:Requiem, so my knowledge of that one is limited to the reviews I read)
Ancient Earth - Predators on (our) Earth, build the first pyramiRAB (which move around inside, kinda like Cube); keep a captured Alien Queen with which to lay alien eggs, which are then hatched for Predators to hunt.
Present Earth - One of these pyramiRAB discovered, hibernating eggs hatch, predators arrive to clean up the mess made by those pesky present day humans and their arctic explorations, one predator infected by the aliens
AVP2 storyline, something involving the Predalien hybrid and some other rubbish. Lots of rain at night and not very well known actors. People die.
The Future - Mining ship discovers the alien eggs on distant planet (plus fossilised Space Jockey), everyone except Ripley dies (oh, and the cat), Ripley goes to sleep in her pants.
Ripley stuck in stasis, eventually found. Returns home 80 odd years after she left. Humans have colonised distant planet, lost contact, Ripley and Marines head there, loaRAB of aliens, all hell breaks loose, biggest and best bitchfight EVER, Ripley, Newt, Hicks, and half a robot survive, go into stasis (because that worked so well last time).
Ripley et al crash on prison planet, Ripley only one left alive from the previous film, EXCEPT FOR stowaway alien(!), Ripley sacrifices herself to save everyone in a beautiful camera shot.
Even further in the future - dead Ripley cloned to get the alien gestating inside her. She's a bit 'different'. In a totally unexpected twist, the aliens wreak havoc. LoaRAB of people die. Also, swimming! that's new. Alien queen created by Ripley's cloned alien DNA gives birth to strange albino.....thing, which is sucked out an airlock, and so was totally worth the puppet cost. Ripley, another robot, maybe a few others? land on future! Earth. Joss Whedon cries at the realisation of what his work became. So do the audience.
So, prequel then? When and where will that be set? Present Earth? Past Earth? Alien homeworld? Planet where we first encounter the alien? Hollywood, where the alien kills everyone involved in the AVP series? And the people behind Alien Resurrection (except Joss)? Or, maybe, for once in Hollywood, the series could be left alone, and AVP, AVP:Requiem, and Alien Resurrection could quietly be forgotten. The Alien films are really Ripley's journey; it would take Scott, Weaver, Cameron possibly (hmmm Aliens in 3D?) before I'd want to go near the series again. (And I LOVE the first 3 films)
So to summarise - Sigourney Weaver, and preferably Ridley Scott AND James Cameron behind the camera (one produce, one direct?). Or go invent a new franchise and stop pissing over 3 great films that tell a story from it's inception to the natural endpoint with ever diminishing sequels/prequels/whatevers.