Putting my rabid fanboy aside for a moment, I can look at this objectively and say Devin Townsend without even thinking about it. No single musician in history has had a more varied career than Devin. Once you find me another musician who has experimented with industrial death metal (though, SYL are pretty much in a league of their own. They defy all classification), pop-punk, ambient drone, ambient nature music, swing metal, pop metal, every single form of metal under the sun (Deconstruction), 60s rock, and the multitude of styles displayed on any of his solo albums, I'll reconsider.
Had you asked me a few years ago, it would be Steven Wilson. The thing about Steven Wilson is that he never plays with very much technicality, which definitely doesn't affect my ability to listen to Porcupine Tree (though, most of it sounds pretty damn boring after being exposed to an album like Deconstruction), but Devin Townsend has proven numerous times that he is a fucking master of the guitar, but he chooses not to display it all the time because he's actually tasteful.
The other Steven Wilson argument would be that he's an amazing songwriter, and while I agree, SW has never written anything that comes close to the level of emotion displayed in The Death of Music.