So totally subjective, and really, an impossible thing to say, because, unless you have a really one-dimensional taste in music, ie you only listen to one particular band/artist, then changing taste and mood will alter what choices are made.
Personally, based on bands I’ve actually seen, and whose music I loved from first hearing, then:
Led Zeppelin
Arcade Fire
Talking Heads
Fleetwood Mac
Elbow
Goldfrapp
Of course, there are loads of really great bands who I love, but it would be difficult to justify labelling them as best band ever, bands like
The Drink
Howling Bells
Belly
Lush
Dinosaur Jr
Metric…
All of whom I’ve seen, whose music I really adore, but I find it really difficult to elevate any to ‘best band ever’.
Arcade Fire may well be, at least for me, possibly the best, their music is beautifully written, played and performed, is intelligent, epic in scope, but their live performances are on a level above pretty much anything I’ve ever seen by anyone else.
With the singular exception of Kate Bush, but she’s really a solo artist.