this is a tough one. i love both of these universes, but they are both so different that it's hard to choose.
Anita Blake has a lot more violence than BTVS does. on BTVS, the vamps dust nice and clean by decapition or a stake through the heart. in Anita's world, you have to stake them AND cut off their head. and they don't dust, just leave behind a messy, bloody corpse.
Anita's world is very male dominant, she's the only female. the role's are reversed in BTVS, Xander ends up as the only male lead.
hmm...this is hard. i think, on the whole, if Antia Blake had been a TV series instead of a novel, i think she might have won in the end. but as it stands, BTVS wins for me, 'cause of the TV series issue...ok, ok, i'm coping out, sue me.