As a guitar player for 50 years, my standard for "greatness" is measured by how many other musicians play your stuff. Jeff Beck wins hands down. Nobody tries to emulate his playing.
+1 (from another guitar player - of 46 years)
I don’t think anybody tries to emulate his playing because nobody CAN emulate his playing. Jimmy Page used to flummox me as a young player, until I discovered his alternate tunings. Jeff Beck? I've never even bothered to try, not once. His style, technique, tones...........simply amazing. Otherworldly. His "Live At Ronnie Scott's" DVD is one for the ages. There's a great Youtube video of him being interviewed about the gig and what he thought the best moments were and why.
And another +1 for Rory Gallagher. Highly, HIGHLY underrated. When someone once asked Hendrix how it felt to be "the greatest guitarist in the world", his reply was "I don't know, go ask Rory Gallagher.”
'Nuff said.