Coming from a global/business perspective there is no doubt that it would be Will.I.Am. Between the tracks that he has produced, written for other artists (think Usher O.M.G.) and all of the hits he has created for the Black Eye Peas and Fergie's solo album he (right now) is the undisputed KING of hooks, because he is hooking the most people in. Second (same angle) would be Bruno Mars.