is this the greatest live band of all time?

Yeah Allan Sherman and Lawrence Welk...At least i got to see the driving horse at the Steel pier too....My Grandmother and Greatgrandmother both of them loved them...i had to be quite of leave the room...lol

Ok. I've seen Springsteen live scores of times going back to his days at local bars in Asbury Park (and at least once every 2 years since then to date). He represents more than half of the top 10 shows I've ever seen. (Elton John and John Lennon for a set at MSG being #1).
But I saw a guy a few times--for the first time years ago because I had read an article in which Bruce said that he was the best live performer  on the planet and that he (Bruce) could not measure up. It was Prince--- who was never a real favorite of mine. Only had and still only have 2 of his albums and don't play them much on the big rig. But live-- the most amazing live performer I've ever seen.  Great guitar player often while doing splits, dancing---coordinated moves in tandem with of all of his players. It was like watching James Brown on steroids only with less sweat. 

Roger Waters The Wall, United Center, Chicago
Yes the Relayer Tour 1976
The Grateful Dead, Hearst Greek Theater, Berkley, 3 shows. Gerry was still with it.
Peter Gabriel, Universal Amphitheater, LA 1982
Emerson, Lake, and Palmer, McNichols Arena, Denver. The Works Tour 
Man I could go on...Smashing Pumpkins Hawkwind, Zappa  Too old. Concerts are a young man's game. And they are so expensive! Saw Allman Brothers for $8, Jethro Tull for $10

The Grateful Dead.

This is like asking what is the best painting ever.....very subjective.
That said, there are many good choices in this thread and I would have a hard time arguing against The Grateful Dead.  The Who (1975) may have been the best concert I have seen, although Johnny Cash was memorable too.  So many good ones - I appreciate the artists who are energized to deliver their best performances in front of a live audience.