The best band of all time, in my view, is YES.
Tho I've always found Emerson, Lake, & Palmer the clear better choice, I've went back and gotten The Yes Album and Close to the Edge recently. CTTE is, clearly, one of the best prog-rock works of all-time IMO. A true work of art.
Can you believe this? In March of 71 my good bud and I went downtown here in Indy and for $6 we had a 3-band lineup to die for at the Tyndal Armory. 1st up? Black Sabbath...they cancelled (who cares, they always seemed to do that at the time and even back then, I liked the heavy sound, but hated that whiney singer...go figure)
So, we opened with YES, right as The Yes Album was released and they opened with Yours Is No Discrase, great set...and the headliners?
Jethro Tull, right as Aqualung was being released so they played alot of Stand Up/Benefit as well...one of THE best shows I've ever seen. Ian Anderson's performance was worth, at least, 10x the price of admission even then.
My $0.02