I would say The Scourge. You get a snazzy obvious metaphor is obvious suit, as opposed to dressing like a Bavarian peasant. And while Lovecraftian horror usually posits breeding a slave hybrid race to replace humanity, wanting to kill all humans and half humans is just standard demon boilerplate. Plus half demons are a stupid idea, or at least one that requires a little more world building. Did a lot of girls join the wrong cult?
Apparently, if you inject fish DNA into people, the hellmouth turns them into were-fish. To me, this seems like the most promising avenue of monster creation.
As for the question of if Werewolves are demon hybrids, eh. Almost everything in the series can be traced back to the Old Ones, except maybe that football frankenstein, Ted and the fishmen. Even Buffy is a demon. But it's never stated outright.
