Probably Alexi Laiho.
For me it's probably Tony Iommi since he had a groundbreaking vision for riffing and Peter Lake for being able to grab the stuff that only goes through the periphery of others minds and put it into practice (hence the name Theory In Practice maybe).
I lean towards Shawn Lane, the man's ability to play guitar and piano at that degree was ridiculous.
I have to say Yngwie.
Jason Becker
Kirk Hammett
I could post a 5 page post right now... But if I have to go with "Best" guitarist look no furthur than Guthrie Govan.