Best "ever"? No idea.. but here are the guitarist I enjoy listening to, playing along with (in my bedroom of course, haha) and have influenced my playing style:

1. David Gilmour (Pink Floyd)
2. Carlos Santana
3. Steve Morse (current Deep Purple guitarist, originally from Lynnard Skynnard)
4. Angus Young (AC/DC)
5. Jimi Hendrix
6. Joe Satriani

and many others...

A completely unknown, to me, guitarist that I have been trying to find more songs with him playing in is Tim Renwick. He has played in so many bands and worked on so many albums that it's seriously not funny.. My first meeting with Tim was on the Pink Floyd PULSE Live DVD.. though now I have heard some of the other songs he's played on, I know that I have heard him many times before. On the DVD, he is just wonderful to listen to.. unfortunately it's David Gilmour that everyone is there to see, so Tim doesn't get to play a lot during that gig.