User blog comment:Zoroman678/If Zoro and Sanji were to go against eachother, who do you think would win?/@comment-3387274-20110803184535

Zoro fights the second strongest of the enemies, while Sanji takes third and Luffy first (as seen with Baroque works and CP9) he also deals far more blows to his opponent, suggesting greater combat ability

However Sanji walks away from his fights with a witty comment, whereas Zoro takes more injuries, and more often ends his fight defeating the opponent, and then falling unconcious himself, as with mr one, Cabaj, and similar.

So I'd say Zoro is tougher, but think it works out very close to fair in the end.