Zombie. We've got guns, and we're smarter, and stuff.
Machines, once they gain intelligence, will promptly end us.
Aliens, if they're smart enough to get here, are smart enough to kill us.
If a meteor is coming, Bruce WIllis is too old and Ben Affleck is too lame to save us.
Zombies. Cuz, remember that time when one guy got rabies in NYC, then EVERYONE suddenly had rabies?
We'd win against zombies. Even I am Legend Zombies.