Its hard to say whos the best guitarist when it comes to any genre of music because every artist arranges their music differently. And theres a difference between being able to shred like a maniac and make music sound so good it brings a tear to your eye BUT

blues id say Eric Clapton or B.B. King. (who doesnt automatically know tears in heaven when they hear it or the thrill is gone). listen to riding with the king if youre a blues fan

classic rock id give it to Jimmy Page (stairway to heaven is such a good god damn song) and Led Zeppelin rocks man.

country i hand it to Mr. Guitar Chet Atkins (tenderly and imagine are great songs)

bluegrass Earl Scruggs is mindblowing although he plays a banjo

Yngwie can shred like a maniac.

And if you think Jean-Claude's the best white martial artist, you havent seen George W. get to drinking and tangoing with Saddam in his holding cell.