Hmm...
PTS Kabuto was supposed to be on Kakashi's level, but Kakashi had a good counter for Zabuza's hidden mist. It was his trademark jutsu, so having a counter for it is a pretty big deal. His best chance is to hide underground but he has to come out eventually. Taijutsu isn't Kabuto's specialty, so it might not be wise to engage him close up. IIRC Kabuto's plan was to tire Tsunade out and restore his chakra so he had an advantage against her. Here, Zabuza isn't going to keep slashing a fleeing Kabuto.
Kabuto has long-range genjutsu but it's more of a quantity over quality type of thing.. I don't think Kabuto would fall for it. Remember that Kakashi's genjutsu would supposed to be subtle. I'll give Kabuto props for his chakra scalpels since Zabuza won't be able to use his sword with torn muscles, but overall my money is on Zabuza unless somebody can change my mind.