Err . . .
Stevie Ray Vaughan? Rory Gallagher? Jeff Beck? John McCaughlin? There'e just so many wonderful gittar players out there, I don't think you can say any one them is "The greatest". Your favourite yes, fair enough. That's a matter of taste. For me it's as much a mood thing as owt else. I have a DGG vinyl of Narcisco Yepes playing Vivaldi's Lute Concerto in G minor transcribed for flamenco guitar. There are times when that feels like the most brilliant piece of music in the known universe and times when it bores my ass off.
I first heard Gilmour backing a singer by name of Sid Barratt.