I mis-read the post--I was thinking what was the best clean tone I'd ever had.
So answering my mis-read D), it was my Strat with Kinman Woodstocks > Fender TBP-1 preamp (basically a Fender Showman preamp) > Rocktron Intellifex > Peavey 50/50 stereo power amp (EL84s) > two cabs (2x12 Avatar with Eminence RW&Bs on one side, "detuned" Vox Baby Beatle 4x12 repro cab on the other side--with a Greenback and a Weber 1265c for the upper two speakers, the bottom two speaker holes left empty)
well, the loudest, cleanest, most tweakable clean i have ever heard is a peavey nashville 1000. 300 watts into a single 15", with a midrange amount and freq knobs, it can sound very fendery or very voxy. REDICULOUSLY loud and clean.
Vince Gill. This was at an outdoor concert. He was playing his Rivera R100s at the time. Both his Strat and Tele sounded incredible with this beautiful bell-like clean tone. The sound was crystal clear, but with so much body and warmth.
James Calvin Wilsey's playing on Chris Isaak's "Wicked Game" album does it for me, as does Mark Knopfler's first few albums with Dire Straits, even though there's some compression going on... Also, honourable mention to the guys playing on the Drive-By Truckers albums - there are some great licks by Cooley, Hood and Isbell, "Decoration Day" being my favourite.
Robbie Blunt. Very recognizable and cool tone. He played with Plant on like four albums, and I know he did the guitar work on Julian Lennon's Vallotte. He also played on Edie Brickell's record, but I don't think he was the guy for What I Am.