Whats the best Apocalypse / Alien invasion movie.

I like the Avatar because the humans are the ass kickers.
I like Prometheus because its sort of believable.
I like Transformers because we get help from the Alens.

so out of all the Zombie movies, natural disaster movies, alien movies (both friendly and hostile aliens), comet movies, spy movies, disease movies, robots taking over movies, What is your favorite one, GLP users?