I am not a guitarist, so I'm not going to try and argue who was "best." But when considering Prince's work, he is a good enough guitarist to be compared to the greats. But he goes further than that. His most recent tour was him playing the piano alone. Have Tommy Emmanuel or Fapy Lafertin gone on tour as a pianist?
Also consider his songwriting catalog. Most artists can do a few albums, but then really struggle to keep creating. Prince released a new album almost every year since 1979. That he had any of those skills would make him famous, but having all of those skills made him one of the giants of American music.
People who like his music like him a great deal I guess. He comes off as a troubled and confused man-boy to me, and after I’m exposed to Prince I get the urge to speak to one of the Mercury 7, or other actual men thereabouts to cleanse my pallet.
And musically, I ONLY commented on his guitar playing ability. He played the guitar with layers of flash and glitz and gloss and shtick because that was “the show” and his fans liked that sort of thing. Maybe he was a great entertainer, but he simply wasn’t a great guitar player... which is why he didn’t just play guitar without augmenting it with visual stimulation.
FYI, I’ve been playing the guitar almost every day for 35 years and I suck compared to Prince, but he then sucks compared to Fapy Laferton and Tommy Emmanuel. It’s all relative, and it may take another guitar player to see it.