i'm glad somebody mentioned jeff beck.
i have heard page, clapton, and beck, all live, in concert (multiple times).
if we are just talking about rock guitarists, and not classical or jazz guitarists, it is hard to beat jeff beck.
I saw all three at the same time at the ARMS Concert (Ronnie Lane's benefit for multiple sclerosis) at the L.A. Forum in '83 (sitting 2nd row center). Beck and his band played the first set, Clapton the second, and Page (with The Firm) played the third. Then the highlight: All three came on stage together to play "Layla" (where they traded off amazing solos) and "With a Little Help from my Friends" (with Joe Cocker on vocals). Amazing show.