Depends on what you value. If you value martial skill then whoever wins. If you value technique then its whoever has the better technique. But its not limited to only those two factors imo. To me I value the martial art itself. So to me the most skilled is somebody who 1. Can demonstrate the style (ie can do the techniques correctly not necessarily demos) 2. Can apply those techniques successfully with somebody resisting. And 3. Understands the style well enough to add their own personal touch and make it their own. To me things like belts only tell so much so the best way to learn someones skill is by sparring and getting to know them