The 90s!!!! Especially the early 90s. The rise of grunge, the excellent noise and garage rock scenes, not to mention several monumental releases in every subgenre of metal, which really diversified a lot in the 90s.

The 70s & the 80s. The 80s had such variety to choose from, along with the introduction of MTV & music videos. Music during the 70s speaks for itself.

'60s. Beatles, Beach Boys, Rolling Stones, Doors, Jimi Hendrix, Kinks, etc.
'50s and '70s are also great. Elvis Presley, Chuck Berry, Buddy Holly, etc. for the former, and Eagles, Queen, Billy Joel, more Beach Boys, more Rolling Stones, etc. for the latter.

I think the 70s and the 80s. I totally agree with Necromancer. These decades had ample variety: there was Led Zeppelin, Black Sabbath, Dixie Dregs (supreme Steve Morse!), Deep Purple, Rush, etc etc in the 70s; then what can we say about the 80s? Van Halen, Eric Johnson, Satriani, Megadeth, Frank Gambale (let's include him here, for he usually fell back on some distortion as well), etc etc. The 90s weren't that bad at all, were they? I may be forgetting to mention lots of top-notch bands indeedy.

Definately 70s

We should say, it was a great era in 60s, 70s and 80s for Rock industry, unless and until Mr.Micheal Jackson came into frame, XD: