It's not really a valid question because guitar playing is an ART, not a competitive sport. How could it be measured? Is Yngwie Malmsteen's incredible speed better than Dave Gilmour's ability to create tasteful and moving solos? John Williams' faultless classical guitar technique is second to none, but, by his own admission, his improvisational skills aren't in the same league as those of his late friend, the Jazz virtuoso, Joe Pass. There's no greatest guitarist - only favourite guitarists.