I like having human antagonists, and when you think about it, it's more realistic that way. Zombies are slow, unintelligent, and can only kill if they get right on top of you. Once they've survived and lived in the zombie apocalypse humans would be able to set themselves up pretty nicely and be able to handle the zombies relatively easily. The more time passes, the less of a threat zombies are.
Other humans, on the other hand, are a much bigger threat. They are capable of deception, they can work in groups, they can harm you from much longer distances, etc. I still want zombies to be a real threat in S2 (and I'm sure they will be), but I'd love to see either a person or another group show up and cause problems for us.