If I had my druthers, I'd say Dumbledore, if only because he's too much of a Deux Ex Machina in the series. It would raise the bar of terror and suspense.
Though now that people mention Hagrid, I can see him being a good possibility.
It just had better not be Ron or Hermoine. (Or Neville or any of the Weasley clan.)
I dunno about Harry not having anything to do with the Dark Arts or protecting against them after growing up. Seems very doubtful to me. Just can't see him "running away" like that. (I too had picked him to become Professor of Defense Against the Dark Arts when he grew up.)
Snape? Also a good possibility, though she likes the character a lot and I think the potential interplay with Harry getting the Prof position that Snape has always coveted is just too sweet. But yeah, makes serious sense that he'd go down - Voldemort has already marked him for death.