Well, a lot of this comes back to everyones own taste and also a bad habit often seen these days that a good guitarist is a fast guitarist. Thats so not true. Too much technique, not enought soul. Offcourse, those who can mix both speed and soul (SRV to name one) are quit impressive and pleasant to hear play :P.

But if you think back and you think in terms of the guy that inspired all the greats of the past 40-50 years ( atleast in blues and classic rock) and whom Keith Richards himself said he was just trying to get to his ankle...

Robert Johnson.

Now thats my vote.