My favorite live year would be between '71 and '72. Especially the Australian/New Zealand tour in '72, the band was on fire the entire time. That being said, '77 was pretty great also (all sloppiness aside.)
The Knebworth shows were fantastic, but can't say that the enitre '79 year was because the first of the two warm-up shows at the Faulkner (sp?) theater was pretty weak. Just listen to the epic sour note in the intro to Nobody's fault But Mine if you don't believe me.
However, everyone has a soft-spot for the blues jams of '68 and '69, and I'm no exception.