Definitely the Organ. One of my best friends is quite the prodigy when it comes to musical ability in general so I know how versatile these skills can be. Learning to play the piano would also be much easier in this case. My favorite music-playing character....I honestly don't have one. I mean the only anime with a focus on music that I have watched is probably "Your lie in April" and I have a lot of problems with the characters there. I can't think of anything else at the moment either...