SRV because I never see his name brought up in conversation, but the guy could destroy most other blues guitarists.
Dimebag because I still feel he's like the new age Kurt Cobain, nobody appreciated him to the full extent until he was gone, IMO.
Hanneman because everyone's too busy looking at King, who I think is a little OVERRATED, just because of his looks. Few people know it was Jeff that wrote "Angel of Death".