This is a toughie...
I've narrowed it to:
Heroes Are Hard To Find (1974)
Shakin' The Cage (1987/88)
white album (1975/76)
...those are the tours on which I caught several shows each. I think I'd have to rate them in that order...1974 being the best. Probably, 99% due to the fact that it was the first tour I'd actually seen them in person. The 75/76 tour was, BY FAR, the best tour I've seen with Lindsey & Stevie.
Of tours I've only heard and not seen...
Bare Trees tour (1972)
Then Play On tour (1970)...
the last days with Peter Green, the band seemed to be playing at their highest (both literally & figuratively 
) level.