Don't forget Punky Meadows!...he's more fluid than Jeff Beck!
Wow! Now I know where Jeff Young got his hairdo!
Well, my hubby is the guitarist of the household, and I'll have to get his take later.
But, for me (one who is outside of so many of the technical aspects), a great rock guitarist -- or musician overall -- is an artist who is truly one with his instrument; i.e., the guitar becomes an extension of the player. Also, their personality must be conducted/personified through their playing.
So, these being my standards, I would have to say that one of the best rock guitar players is -- in my heart -- Criss Oliva