Gonna go with Parker. Him surviving would at least be logical. If he had just flamed the xeno and Lambert, he and Ripley could have both made it to the lifeboat, and possibly even save the Nostromo entirely. Of course he'd come off as a cold-hearted bastard, but he'd be alive.
Still, I'm all for how Alien turned out. There's nothing about the movie that I'd change, not even the special effects and bad 70s computers. Keep it all.