It's a crappy question
Obviously no one could *really* be idiotic enough to think the Beatles or Pink Floyd are the 'worst band ever' - people are bound to end up thinking of 'most overrated' instead. But then the actual worst bands are going to be the ones no one has heard of, so...

I vote that we instead go for 'best obscure band that I love and many people don't know about'. In which category, and in no particular order, I shall examine my Spotify playlists and enjoin you all to lend an ear to

Porcupine Tree (best song 'Time Flies')
Brand X ('Disco Suicide')
Spiritualized ('Out of Sight')
The Dukes of Stratosphear ('Mole from the Ministry')
Sneaker Pimps ('6 Underground')
Television ('Little Johnny Jewel')

/edit
For a bit of fun, here's a playlist I put together of music that I vaguely think of as 'epic' - by which I mostly mean pieces that build up from small beginnings into bigger and broader soundscapes. Most of the ones listed are on it, as well as a fair few classical ones.
( flatfrog Staring vacantly into space, Thu 30 Dec 2010, 13:40, 12 replies)

In my post down there I mention The hold steady at the Counting Crows concert I went to.
On the other side of this, the other support band "Blind Pilot" who, when they came out on stage I thought would be crap, turned out to be fantastic.
Really, REALLY good. I'd happily have paid just to go see them.
( Maffers I flow kinda strange like Spina Bifida footprints, Thu 30 Dec 2010, 13:46, closed)

I was a big fan of Porcupine Tree many years ago
I've seen them live a few times. And Spiritualised.
( The Light in Chains don't touch the Pope's boner, Thu 30 Dec 2010, 13:47, closed)

Read this wrong
And almost became angry as I thought you had included Television as one of the worse bands ever. But you didn't so I feel validated by that.
(muzzvsworld, Thu 30 Dec 2010, 14:00, closed)

question:
How many hipsters does it take to change a lightbulb?
( Not Pineapple anymore, Thu 30 Dec 2010, 14:01, closed)

I only discovered them very recently
Through a link on Ben Goldacre's site. Listened to them obsessively for a couple of days.
( flatfrog Staring vacantly into space, Thu 30 Dec 2010, 14:07, closed)

I've heard that Sneaker Pimps song so many times before, and not known its name.

( Bourbon Fox Bourbon is a moron, Thu 30 Dec 2010, 14:04, closed)

heavy vegetable and built to spill aren't well known enough
www.youtube.com/watch?v=VtgYvUpto4M

www.youtube.com/watch?v=ShrlKZUVbRQ
(chocolatelemming, Thu 30 Dec 2010, 14:19, closed)

Porcupine Tree
made me waste about £20 on 2 albums that were recommended to me.

They are truly, truly awful.

I vote Tool - Lateralus, but then I expect a fair few people have heard of them.
(Yagememnon, Thu 30 Dec 2010, 14:35, closed)

This is why I love Spotify
No need to waste money - just check them out and if you like them, keep listening.

Ooh - just listened to that song - thumbs up to that, thanks :) Annoyingly, they're *not* on Spotify
( flatfrog Staring vacantly into space, Thu 30 Dec 2010, 14:45, closed)

I did the same. Was given some of their stuff but didn't really like it. Preferred Tool (Lateralus is incredible)
(RJWEcology is just sharpening his axe on, Thu 30 Dec 2010, 14:52, closed)

I do like Sneaker pimps a bit
but prefer IAMX
( Amberl was stripey and dominated Europe, Thu 30 Dec 2010, 15:01, closed)

Side projects
It's interesting how often musicians' side projects are better than their famous bands. Three of the bands in my list are side projects (Porcupine Tree, Brand X and Dukes of Stratosphear) and there are quite a few other examples (Gorrilaz being one that springs to mind). I guess it's not that surprising, really.

Not that bothered by IAMX myself, though.
( flatfrog Staring vacantly into space, Thu 30 Dec 2010, 15:07, closed)

I
Fucking love Sneaker Pimps. Thanks for reminding me they exist!
(Megamoss, Thu 30 Dec 2010, 16:12, closed)

AMPLIFIER
Anything by these guys, esp their eponymous debut and recent hard to find double CD The Octopus. Best rock band in the world!
(Styubud, Fri 31 Dec 2010, 17:36, closed)

do you mean:
www.youtube.com/watch?v=66v-eevWwyY

i like them
(chocolatelemming, Fri 31 Dec 2010, 17:44, closed)