Jeff Buckley without a doubt. I don't care how many Hollywood starlets or American Idol douchers have co-opted his legacy, dude was an incredible and technically, proficient guitarist who had the best pipes in the history of rock. I challenge anyone to both play and sing "Grace".
Drowned in the Mississippi River while spending some time recording in Memphis at the age of 30. Was not a druggie or a boozer. Son of folk legend Tim Buckley who never gave a crap about him while Jeff was growing up. He, ultimately, was better than his father.