For me it has to be Cream, I think they pioneered the sound that Led Zeppelin got a lot of the credit for, and the trio are all some the best at their instruments that exist in my opinion. My only criticisms would be that Gingers drumming is downright boring without accompiniant and that his drum solo on Toad is too long.
That said Led Zeppelin, The Who, The Rolling Stones and Pink Floyd are up there and are my top depending on my mood.
My least favourite band (excluding the ones I have absolutely no respect for and who I don't believe deserve to be called a band (One Direction, Nickleback) would have to be the Doors, I don't mind their music on an instrumental level, but Jim Morrison is a terrible lyricist. This wouldn't neccesarilly be a bad thing (I'm Glad by Cream is embarassing for everyone involved lyrically) but judgiing from his awful poetry and awkward live performance he really thought he was writing Bob Dylan or Shakespeare or something. I don't think they deserve the fame, popularity and iconic status they have when better bands from the era like Grateful Dead and the Yardbirds are largely absent from popular culture.