Probably the Upgrade, because it doesn't make sense even conceptually. Like, yes, it's superior because it has bulletproof armor and can turn invisible... just like every other Predator.
EDIT: I also hate the AVPR Predalien with a passion. I can still remember the news that a picture of the Predalien from the new movie had leaked, excitedly clicking the link, and seeing... that. That was the moment I really knew we were in trouble.
Also, I know this is a LEAST favorite thread, but my favorite spin on an older design is the Deacon, because I like to imagine that it's a Xenomorph that's crap at being a xenomorph. Like, it's blood will sting, but nothing beyond first degree burns; It can stick to things, but not solidly enough to climb walls; it's not particularly dangerous, but it will f**k with you psychologically. I view it as a cross between Stripe from Gremlins and Wile. E. Coyote.
He'll steal your wrench and then bite you when you try to take it back, but he's not taking over any colonies.