I much preferred the original 'Batman vs Predator' out of any of the Batman crossovers, although 'Batman vs Aliens' is okay. Batman vs Predator 2 and 3 have their moments (like the Predator being unable to see Mr. Freeze in thermal vision, that was clever) but on the whole they're not as good as the original.
The original Judge Dredd crossovers were a good time (l liked the Aliens one more than the Predator one); I have the trade paperback for the new series but haven't gotten around to reading it yet.
I remember Green Lantern vs Aliens being pretty neat and I've been meaning to re-read it.
The Top Cow half of the Witchblade/Darkness/Aliens/Predator crossover is entertaining, mostly because the Top Cow writers and artists fully embraced how ridiculous the crossover was and just dialed the insanity to 11 because who really cares. The Dark Horse half of the crossover took itself really seriously and, uh, the results weren't good.
Aliens vs Predator vs Terminator is real bad - it's one of the few series that I don't have every issue for. Every once in a while the completionist in me says "hey, maybe you should complete the series", and then I'll re-read the issues I have and remember why I don't.