Lots of old guitarist listed but I believe there is no greatest number 1 guitarist of all time. They all have their strengths and weaknesses but they all also steal from each other. I prefer more original sounding guitarist no matter if they play fast, slow, melodic, heavy, or just all over the place. Here's a few of my favorites.

David Gilmour-most melodic with emotion to create a feeling using modes especially dorian

Jack White- master of Big Muff pedal and takes simple power chords and pentatonic scale to create

Ed Sheeran- if you haven't seen him play with loop pedal acoustic then your missing out. Dude can really make some music. Laugh at him but he's without a doubt super talented when he performs by himself.

Adam Jones- the architect of Tool

Junior Kimbrough- my favorite blues guitarist. Love playing his style.