Tough one, but I'm gonna go with Predators. It's getting better with age, I think. Alien3 is great, but has too many issues that (I guess for fans) take you out of the movie.
I enjoy the fact that Predators acknowledges and respects its franchise history ( I don't want to go down the "and repeats it" argument road!) and adds some new ideas which I thought were great.
And it has Danny Trejo.