I know that their is no real answer to this question because it depends on the individual. But for discussion purposes, what is your opinion and why? The bass has popping, slapping and thumping! The guitar has strumming, chords and a tiny neck and strings and requires a pick! The drums are physically exhausting and requires timing! The keyboard requires both hands to function independantly! To me, the guitar is the hardest! They make them so damn small! I can wrap my index finger around the whole neck and I cant use a pick to save my life!