It's a tough question, since the guitar is an incredibly versatile instrument and is capable of being used for a wide variety of genres.
You have your Satriani, Malmsteen, and Vai... they're fundamentally incredible, but there's really NO substance at all. It's just complicated music sheets.
You have your Stevie Ray, Robert Johnson, and BB King... great blend of soul, substance, and talent.
Then you have your innovators like Omar-Rodriguez Lopez, Robert Fripp, and Peter Banks. They're normally acquired tastes, but there's a nebulous cloud of awesome to be had there.
Then of course you have Jimmy Page, Hendrix, and Chuck Berry. They really speak for themselves, but they appear to be the perfect balance of everything one looks for in a great picker.