My money's on the zombies, unless the vampires think to use distance weapons. If all they use is teeth and claws, I think they are toast.
Other fantasy episodes of DW that we would like to see:
1. Harry Potter vs Luke Skywalker.
2. Emperor Palpatine vs voldemort.
3. I personally would like to see vortecien mages vs Death-Eaters. Vorteciens are evil wizards from children of the Phoenix, a collaborative writing project I used to participate in. I'd fight a Death-Eater. I'd kill myself to prevent being taken alive by a vortecien. That's how scary vorteciens are.
4. Predator vs Alien, but that's already been done.
5. Hanial Lecter vs Dexter Morgan.
6. The Transporter (Jason Statham) vs the guy in Drive, the movie.
7. The Serenity crew vs the Maquis.
8. Pernese dragons vs Naomi Novik's dragons (except I love both!)
9. Kzinti vs Klingons.
10. Drow elves vs ?
11. Severus Snape vs Darth Vader.
12. Captain Kirk vs Captain Malcolm Reynolds.