Isn't this a thread that's been covered 1000 times before? Ah well.
Personally I think it's down to P1 & P2, very hard to call. The original was a calculating hunter, picking off his highly trained adversaries one at a time, he showed alot of cunning & patience in his actions. The second Predator on the other hand was a much more frontal assault kind of killer, preferring to just slaughter everyone with much more high powered & savage weaponry. They both had very different, but very effective hunting techniques, far above what we have seen in most of the other movies.