Re: "greatest guitarists"... just my opinion, technical expertise does not necessarily make one a "great guitarist."
Keith Richards may be just a riffmeister, but he's the best riffmeister ever, probably. He brings exactly the right thing to his band, and always at the right time. I think he fully deserves to be #5 on that list or any list. IMO, it's not always how fast or how adroitly one can move his fingers around the guitar neck, or how long the guitar solo is. (And if the solo is longer than about 20 or 30 seconds, please, just kill me.)
Stevie Ray Vaughan always makes the lists of "great guitarists"...but I find him derivative, recycled Hendrix for the most part. By comparison, his brother is a way tastier player in my mind. Hendrix himself was innovative in some ways, if you go for that sort of sound (I don't). Don't even get me started on Clapton.
Then again, I like trashy, three-chord songs that clock in at under two and a half minutes. So, disregard.