Tone

[frank]

Just listening to AC/DC's Powerage and I've gotta say that Malcolm and Angus had the best guitar tone in rock.

SG/Gretsch through a slightly overdriven 60s Marshall. Awesome.

 

[Jonotallica]

Too much mid ranges for my liking, but a very good tone none the less.

 

[Ron Jeremy]

Eddies "brown sound" was the most distinctive and most documented sound in rock.

 

[SpaceMonkey]

I don't think there is any such thing as the perfect guitar tone. If there was everybody would be going for the same sound, and rock would be pretty boring. The great think about the guitar is that musicians continually come up with new and unique sounds. Rather than say one is the best it would be better just to nominate bands and albums that had a particularly great sound on them.
One thing a lot of people underappreciate is the influence of producers and engineers on a band's sound. There are some producers who consistently get a great sound on the albums they produce and whose work is often more recognisable than the bands they produce. I'll stick to metal stuff and name a few producers who had distictive sounds and produced some classic stuff:

Tomas Skogsberg
Colin Richardson
Eirik "Pytten" Hundvin
Peter Taatgren
Randy Burns
Scott Burns (don't like his style though)
Fleming Rassmussen