Poll
42%
21%
37%
Vampires have the speed, strength and cunning to overtake the other two species (not to mention the ability to fly and turn into smoke). The fact that they are vulnerable in the daytime would be a small price to pay; as long as they were inaccessible during those times (say, nestled in a cave atop a mountain), the others couldn't touch them.
Zombies are slow and stupid. They may be "unkillable" in the traditional sense, but vampires could figure out a way to beat them. They could swoop down, grab them by the ankles and dump them into a volcano or something (burning them to cinders, a la "Return of the Living Dead"😉.
Werewolves may have comparable strength and speed, but they can't fly, and they're too animalistic to ever get really organized. Besides, three weeks per month the werewolves would still be human, and the vampires could slaughter them then.