Rankings, barf. Musical genius is such a culturally determined characteristic I'm skeptical of any so-called objective ranking. The fact that most people can't listen to Schoenberg or Webern without cringing, despite their intellectual brilliance, seems to me an open and shut reason why we shouldn't try to pursue the goose-chase of who's the best. Like sure Bach, Mozart, Beethoven, Wagner, sure, they're great, but who's to say that Schubert isn't subtler than Beethoven? That Haydn isn't sneakier and more humorous than Mozart?
We're all just looking around comparing lists with purported experts, trying to have the most respectable taste, the most clever judgment. I studied English under Bevington at Chicago, and he mentioned to me that at recent Chinese literature conferences, academics were sitting around debating who the best writers were in an utterly tedious, frivolous, and pointless exercise.