The only good Predator is the first one, easy 9/10 movie, imo.
Predator 2 made the Predator too much like a superhuman slasher villain, crashing through building walls, tanking liquid nitrogen, and taking lighting bolts and shit. Not a bad movie compared with the rest of the series but a weak follow-up compared to the original (especially when it's contemporary series it's always compared with in Alien, Terminator, and Robocop had better follow-ups).
Predators at least had an interesting premise and tried to bring it closer to the original movie with a group of killers instead of soldiers so while it wasn't great it was at least interesting and didn't have any big screw-ups.
The Predator felt nothing like a Predator movie, easily the worst of the lot.
Prey had an interesting premise but cut out way too much believability on several fronts and made this waifish little girl the warrior heroine and she did way too many unbelievable things (barely looked like like a native too, heck she looked more white than most mestizos and a hell of a lot more white than the girl from the original Predator). They could have made it a good movie but as it is it was a concept that failed (much like say Halloween Ends, though Prey wasn't that ridiculous).