Josh Homme is a good guitarist for sure, but he can never be the coolest, he's Ginger. My vote goes to Jimi, You can tell it's effortless, Slash tries a little too hard, Lemmy's just to f**king ugly, and stupid. Prince shows off just a bit too much, and is a control freak, and that ain't cool, Zappa? to 'out there' to be properly cool, Everyone else mentioned here is too minor league to be king (or queen) of cool
But Jimi? c'mon…The guitarist from soft machine challenged him to a guitar duel and reluctantly Jimi agrees, Larry Nowlin plays this intricate 10 minute prog-jazz solo, hits every note, scales and arpeggios; seriously detailed knowledge, every note played flawlessly, Hendrix responds by turning his amp up to 10; plays one chord, and manipulates the resultant feedback. Huge understanding of what an electric guitar should be used for, something earthy loud, and exhilarating. Not playing loads of fret board wankery.
Cool.
40 years on, and people are still trying to measure themselves against him..