There are two basic ways to determine the “winner” of a presidential debate. One method is by following some set of debate rules, as they do in high-school and college debating societies, e.g., who cited the most facts, who marshalled the best arguments, et al. The other method is to look at the polls following the debates to see who is more likely to win the election. By that measure, there is one clear winner: Hillary.
Having said all that, I think CTLawyer has the best answer.