I think MO head has it exactly right: trying to pick "the best guitarist" is like trying to pick the best color. All anyone really picks are the people who appeal to them.
I like Garcia, obviously, but I don't think he's the "best." I don't think he thought he was the best. What I like about him is how distinctive he was, and that trait, his voice, is really more important than anything else. Put on a blindfold and ask 100 well-known guitar players to improvise eight bars on a borrowed guitar and chances are you'll mistake a lot of them for someone else. Stevie Ray Vaughn often sounds like Hendrix, Clapton or Bloomfield like B.B. King. But no one with even a passing familiarity with Garcia would ever mistake him for anyone but Jerry Garcia.
There are others as well that I like for the same reason, although they are not ncessarily anyone's common idea of a "guitar god." Willie Nelson has a wonderful, idiosyncratic, sort of arpeggiated, strumming lead style. Steve Cropper of Booker T. and the M.G.s is a rhythm machine, and I don't think he's played more than three solos in his entire career. Weir is a great rhythm player with a style all his own.
Then there are others who leave me cold. I'm not a big fan of Eddie Van Halen, although I'll admit I'm not as familiar with his body of work as I might be. I recognize what a huge talent he has, and after one of his solos I feel like I've been through a ringer, it's so fast and furious. But I'd like to hear him just play a solo some time, without the all the feedback, the tapping, and the blazing through every scale to man over a 2-bar break. He always sounds like he's showing off, which is a big problem with a lot of rock musicians, in my view.[/i]
There still is nothing like a Grateful Dead concert