I've read all of the drafts - Red, Ward, Picket, Twohy, Gibson, etc. and honestly think the script we got was probably the best of the lot.
Gibson's should be used as a good example of why Hicks had to die: He turned into John freaking McClane in space. He even said that his script was pretty much Die Hard in space anyway. And the airborne Alien spores, upgrading Aliens ... ew.
Red's script was a mess. Looked like it'd been written by an epileptic five years old. And all the Alien mutations were ludicrous. Set in a small mid-western town ... IN SPACE! Dun dun duuun.
Ward's was okay. Illogical in places, and the animal Aliens just ... wow. God no. But for the most part, okay.
Picket's was hacked up and made into the movie.
Twohy's was pretty decent, but again with the poor creature Aliens. And the Alien being able to dislocate itself and squeeze through metal bars didn't seem to make any sense.