The worst are The Predator and AvPR.
AvP I'll always give SOME props to for going the opposite way with the matchup. One Alien killing two Predators, and no humanized broken tusk pred character (I think they tried with scar or whatever they called him but they could hardly write human characters so I don't count it), nobody saw that coming on release. It was soulless, with nonsensical things like the accelerated lifecycle that you literally didn't need to include, wooden characters who nobody gave AF about, and stupid death scenes like Weyland's, but it is still somewhat watchable to me. It's like the new version of MK. Old MK was better, but new MK was a trainwreck that I couldn't stop watching.
That said it was big wrestling predators against cgi Aliens. They did an advert for the movie in a college football game where the announcers kind of act like salesman for the movie (generally nothing more than, "looks interesting, can't wait to see it when its out,") and they showed the predator slinging the Alien around by its tail, and you could tell that both announcers thought it was so stupid that they were flabbergasted as to what to say. Finally one of them finished with (and I paraphrase), "Gee it looks like that one guy rung his bell," and that was it. It made me lol.