Well there's no objective way to define who's best. Now if you tell me someone is objectively better than anyone else in speed of playing the guitar, or in the amount of time they've played it for or in the number of songs they've written or in the innovation of manufacturing a guitar, they're all quantifiable. When you're talking about David Gilmour as objectively being the best, that's ridiculous. I love David Gilmour. But anyone who says he's objectively the best? That's ridiculous.
Plus I don't even like Slash that much.