Hiruzen takes this.
Hiruzen stomps zabuza in terms of taijutsu, Kenjutsu, Finjutsu, and Ninjutsu.
1. Zabuza has Mist, but that isn't really effective when hiruzen can still locate him thru smell.
2. The executioner blade is useless against Enma.
3. We have already seen hiruzen battle and counter a opponent with far better suiton skills then zabuza, and successfully hold his own.
Zabuza's chakra is not as powerful as Hiruzen's as well, so even if hiruzen did use his dragon flame, it would take zabuza more effort to counter it then hiruzen actually using it. An example of this is when Madara used great fire annihilation and it took 5+ shinobi to use collaborate suiton techs to cancel the jutsu.
Hiruzen can beat zabuza in my opinion with low difficulty. He has already shown analyzing feats and battle intelligence. With enma as his partner zabuza cant win.