As usual, the posts here seem to lack a broad range of artists when the term "greatest" or "best" are thrown around.
How can you make a list that is made of exclusively of guys from one genre? One style of music? I realize the OP titled the thread 'best rock guitarist' but the posts that followed listed guys that are not of that genre.
Every genre needs to be looked upon when you compile a list of this sort, really. Guys like Charlie Christian may not have been rock, but certainly influenced those guys. Without Jimi Hendrix you wouldn't have half the theatrics in music today, nor would you even have Jimi without Buddy Guy!
Music moves in a somewhat linear fashion. You don't really get from point A to point Z without having the rest of the alphabet.
And then there's the the issue of categorizing certain players. One guy has Gary Moore as a rock player- that's certainly correct. Another has Mr. Moore as a blues player. While he did make "blues" albums, he is not blues! Just because you play a blues scale and make a weird face while doing so, does not make you a blues player. Scott Henderson, a very talented cat in his own genre and for what he does, has a video where he's talking about playing blues and while his words say one thing, the "blues" he claims to play is that of what drips from a wetback's ass after a night of drinking during a burrito party.....