Boys, don't get your panties in a wad. I'm not considering these Nickelback and Dimehead or whoever flash-in-the-pan bands you kids listen to. Don't even know them. When I say "worst band ever" I clearly mean long-running, mystifyingly critically acclaimed acts.
And for the record, the correct answer here is "Chili Peppers". While both bands are horrible, just horrible, Chili Peppers are slightly more horrible. R.E.M. managed to fumble out one excellent song in their decades-long reign of terror ("Man on the moon") and maybe one other listenable tune, while the Chili Peppers are just 100% unremittingly unbearable.