If you play Activision's Guitar Hero competitively, you might struggle to beat Cythbot, which can score 99%, and typically manages 75-80%. It's not a humanoid robot but an electromechanical device developed by Cyth Systems to show off its expertise in image processing and integration at exhibitions etc. The input comes from a camera focused on the screen, and the notes are played by pneumatic fingers. Wired Blogs explains how it works.