As an avid music fan myself, and a guitar player...this is a great topic.
If we are going to talk about the BEST guitarist ever...then we need to look at who had the biggest impact, with the greatest ability.
This is a very hard topic, and I like the Duane Allman suggestion. The Allmans are one of my top 5 favorite bands...but I do not think he is the greatest guitarist of all time.
I would look more in the direction of Hendrix.
He did so much for music, and he was an incredible player who studied hard before hitting the mainstream. He knew his instrument like the back of his hand. It was like an extension of his body for him.
After him...Stevie Ray, Jimmy Page, Clapton
their are so many names...and so many different types of guitar. we could move into metal with Randy Rhoads, Zakk Wylde, and Kirk Hammet...or move into blues, as I already did, with Clapton (who fits many genres), SRV, Buddy Guy, Robert Johnson, and even Page who was more rock. Then we have Eddie Van Halen who is in a class of his own...
Then their is Joe Satriani, Steve Vai, and Yngwie Malmsteen who most non guitarists do not know...but are the top 3 best guitar players currently.
here are some more names
Really a great thread idea...there are so many names, I think this will be a great discussion!!!
And remember...it is all subjective