Actually, I would have to say Ender - not because of any lack of respect for Chuck's skills, but rather because they have very different notions of "win" and "morality". Ender is a pre-emptive type, who, if he feels he might be threatened, would attack and fight to the death - his definition of "win" being "opponent will never be able to attack again" - Chuck, on the other hand, would stop when he felt he had gained a clear win - his definition of "win" being "clear superiority without total destruction of opponent". So while Chuck has the more refined skills, Ender's different morality would, I think, lead to a more permanent "win".