I'm fine with both.
If we deploy entirely different teams, we could just say we're dealing with both at once. For instance, you wouldn't want Mechs and Tanks for Ravenloft and Castlevania, but they'd do just fine against zombies.
People weak to Fear, or people who aren't very strong individually, are also better suited to the Zombies - as there's less stuff that comes out of the goddamn walls and rapes you.
That said, our Heroes and many of our "I've seen some shit" veterans are well suited to Castlevania.
So, here's the plan:
Send the Mechs, the Recruits, Star-Lord, the UNITs, BLU Team, half the White Mages, half the Aurors, that Ranger dude, and the X-commies across to the Zombie Apocalypse.
The Knights Inductor (with Darius), the other half of the White Mages & Aurors, Abjurers, Psions, Sandmen, SCPs, Tosh, and Delta Greens should be preapred to deploy to Castlevania (but not all at once).
Egon and the Farseers are staying on ship, owing to their SCIENCE! and Telepathy powers being useful there.