I'd say Christopher Drake, IF
he ever moves onto major motion pictures. He's doing the new Arkham Origins game score aswell. I particularly like his music for Batman: Under The Red Hood, All-Star Superman & The Dark Knight Returns.
James Horner's Spider-Man theme doesn't come close to Elfman's and it couldn't have been that great if he's being replaced by Zimmer for the sequel.
It's surely going to be Hans again and since this is meant to be a different Batman, I'd like to hear something new from Zimmer. Something similar to Drake's work, if possible.