I think that the original response is a little unfair given the self-proclaimed inexperience of the questioner.
It all largely comes down to a matter of taste. Music buyers (you and me) on the whole don't buy CDs because someone's won some Grammys and so forth. We buy it for the feel, the groove, the thrill, the excitement.
Clapton is revered because of his playing in the '60s with John Mayall, Cream, hanging out with Hendrix, his solo work in the '70s, and, of course: Layla (deh-deh-deh daah...). England during the 1960s boasted guitarists of the calibre of Jeff Beck, Peter Green, Keith Richards, Blackmore, Iommi, Pete Townsend, Jimmy Page, and at his best with the Bluesbreakers and with Cream, Clapton was the best of the lot. I wasn't around in the '60, but these guitarists are still revered to this day. Guitarists who followed, for example, Peter Frampton, Brian May or Mark Knopfler, are considered to be very good but can never be the same. It is like comparing the writing of, I don't know, say, The West Wing or The Sopranos with Shakespeare. They may be very good, with touches of excellence, but they can never, however unfairly, reach the pinnacle.
BB King belongs to a whole different tradition, to a time of segregation, and a world that has hopefully passed forevermore. King was born in 1925 so the Abolition could still have been within living memory to those around him. King's music reaches back to artists such as Howlin Wolf, Muddy Waters, Bill Broonzy, way, way back to Charlie Patton and Elder Burch. If you can, check out the American Epic series.
King was as part of the Blues in the post-war years as Clapton was of the 1960s.
Mayer on the other hand is just a bit dull and boring. Technical proficiency is not the same as thrill and excitement.
To people growing up in the 1990s Prince or Slash or Cobain may well be the guitar idol of taste.
In the end, it all comes down to a matter of personal taste.