Elliot Smith seems like an interesting guy, but there's always Kurt Kobain or J Mascis just cuz I love his stuff, Tupac would be great, but altogether I would say Robert Johnson. He's a great early blues artist and seems like an interesting fella.
Also post what age you would want to interview them.
For me: Issac Brock during the release of Building Nothing Out of Something (22 I believe). I think that at this age Issac started to contemplate life, death and everything in between. He would be great.