Werewolf Apocalypse
We've seen plenty of Zombie Apocalypses and even a few Vampire Apocalypses. With the exception of a few stories set on the Moon I don't think we've had an account of a Werewolf Apocalypse. Depending on the type of werewolf plague that gets unleashed I'd find that scarier than either Zombies or Vampires. Zombies, even the fast kind, aren't very bright and aren't terribly strong. Vampires are worse than Zombies but I've less disturbed by something that kills me by sucking my blood than I am by something that will eat me alive.
Werewolves? Even the full moon only variety are:
Fast.
Relatively smart.
Superstrong.
And they eat you alive.