I stopped by TRU and they had the new Aliens wave, and I found replacement figures that were better than the ones I got from Amazon. The '79 Alien's teeth look a lot better and fit together better (although there's a miniscule gap between the front of the upper and lower jaws when the mouth is closed). The teeth aren't perfect, but it's nothing a tiny bit of paint won't fix.
The Blue Warrior I picked up is also a vast improvement. his shins aren't all warped, his teeth line up much better (although not perfectly), and the seam on the head isn't as bad. The seam is still there, so I'll likely sand it down a little bit, and the lower jaw is still a little cockeyed, but it's not anywhere near as bad as the first one I got.
They had a few to choose from at the TRU I went to, and all of the Blue Warriors had the same visibly cockeyed lower jaw; the one I bought was the "best" of the three they had. The other two were about as bad as the first one I'd gotten.
It's weird because my other Aliens in the same mold don't have that problem. I've got the red and black ones from the Genocide two-pack and they're fine.