For purposes of this thread, science fiction counts as fantasy, and so do comic books; I also think we should restrict ourselves to action/mystery/detective series. It's obvious that neither Superman nor Odo is going to be bothered by a Buffyverse vamp, while Roseanne Connor and Michael Steadman are both toast. Also, let's assume that the characters do not know that vampires are real before they're set upon by Spike or Drusilla.
Would get killed in short order:
Monk, Natalie, and their two police buddies. Monk's only chance of survival is the possibility that the vamps in question would be so irritated by him that they'd decide even killing him would involve spending more time in his presence than it was worth. Natalie probably gets or turned. The captain & Randy are as dead as Roseanne.
Fifty-fifty chance of survival:
Gibbs, from NCIS. But not his team. Ducky, Palmer, & McGee get killed quickly, as does Tony; the instant Ziva thinks the latter is dead, she'll go into berserker mode. If it's Spike she's fighting, she might impress him enough so that he'll turn her. Gibbs might make it through; he's tough and very pragmatic; if he doesn't killed immediately, he may well figure out what's up and manage to escape.
Owns the vampires:
Jack Bauer, obviously.
I'm not sure what happens with Chuck Norris.