I give the edge to Zabuza. Zabuza's taijutsu is superior to hers, though her strength obviously tops his own. He can maintain long range, if he chooses. Also while Katsuya is formidable she is far from an advanced battle summon imo, and her seal is meaningless if she can't hit him. I think she can deal with the mist better than her detractors believe, but not as well as her supporters believe. I feel with more range, superior physical skill, experience, kenjutsu and proficiency at killing. Zabuza lops off her head before she has a chance to mount any effective offense, her best shot would be genjutsu imo. Even with that though he still decapitates her, Zabuza was an incredibly formidable shinobi and one of the main factors contributing to his defeat was his delay in finishing the fight. In a fight between Zabuza and Sakura to the death, I think Sakura impresses him with her strength and Katsuya poses a threat but in the end her head rolls.