For musical ability, knowledge and experience, try Gunther Schuller or Pierre Boulez. This isn't to say that these guys haven't written a whole lot of unlistenable junk in their lives, but due to the school I attented, I had the opportunity to work with them in person (as well as a few other notables, such as Lukas Foss and John Corigliano), and these two stand out as the most amazing musical phenomenon I have ever seen. But if you insist on pop music, I suggest Tiffany.
Best musician in the world?
A question posed in another thread, in my view, although musicianship is hardly a sport to be measured as such, the most universally prodigious musician is probably Shawn Lane. He is definitely the world's most phenomenal/inimitable electric guitarist. And he is a world-class pianist and saxaphonist as well.