Ansem and Sora have not met or fought much, but since Sora is the main Hero and Ansem is/was the main villain these two had to fight sooner or later. Ansem has the power of darkness at his command. Of course Sora has Final Form and with it he can slash rings around Ansem. Not to mention that he also has Master Form. It’d be pretty tough to take him down Ansem takes the loss, but he will be back. Sora wins.