i also really like 5/26/77 and 11/6/77
77 was the best year i think
here's how i conceptualize the eras of the dead
late 60s up to 71 there were some awesome acoustic/electric split shows and they were doing a lot of folk and country tunes
for a while they rocked the two drummer two keyboard combo with pigpen and constanten, and Live/Dead in 69 is also outstanding
starting in the 70s they got Robert Hunter writing lyrics for them and a new era really began with Workingman's Dead and American Beauty
Mickey left the band for a few years in the early 70s bc his dad, who managed their finances, was stealing from the band, and instead of replacing him they added keith, which would eventually bring donna
pigpen's death in london in 72 was really the end of the first era of the dead, and 72 had three incredible releases, europe 72, blues for allah, and wake of the flood
the latter half of the 70s was the least commercially successful but the most creative imo, with terrapin station and then really incorporating more funk into their sound with shakedown street
keith died in a car accident in 80, and donna left the band then, and brent joined, and in the 80s they had some mainstream radio success with touch of gray. the wheels start to come off (for me anyway) with brent's death in 90.
i personally think the most interesting period is the second half of the 70s, but you can go deep on nearly any 3 year stretch of their career and dig into different sounds their lineup were bringing
say what you will about donna, but the stretch from 74-79 was the most stable the band was with mickey back and donna and keith bringing the harmonies