Should have to be Zbik. He is the interim champ. Pretty unnecessary fight though, Zbik will get destroyed and he knows it.
I imagine that (a) Zbik's camp will postpone the fight as long as possible, and (b) with Pavlik needing some name fights, Bobfather would probably sooner have him drop the belt than fight Zbik, who isn't even as marketable as Espino or Lockett.
I guess this would be interesting in one respect. They wouldn't give Kelly another month for his hand but the prospect of losing their income from him altogether might be too much for them to handle.