I can't think of any guitar player that exceeds in both.
Duane Allman : listen to live at filmore east or the Layla album, and you will hear that he was amazing both on slide (layla, too late, key to the highway) and fret playing (little wing, love so bad, anyday)
Ry Cooder : of course a great slide player, but his rthyhm work on "very things that makes you rich" is outstanding ihmo
Derek Truck can play great fret playing too
I agree about Gallagher too
oh and I forgot the great Mick Taylor. A very underestimaed guitarist. amzing both on slide and fret, and during the same track (e.g. sway)