I think they are both useful for all guitarists. If you are strictly one and not the other you shouldn't make a band because with one sound and style you won't get any gigs. For listening I perfer the blues because I can only put it one way. Hendrix, Stevie, and Clapton all came off of and played the blues. And look at the shredders Eddie Van Halen and Yngwie. Eddie is a bit of and asshole to his fans and Yngwie is a major asshole to his fans. Blues men are nice guys.