The Moody Blues. Can't think of an Moodies album that didn't have at least few songs I liked, and nothing of theirs has ever rated l"OMG I can't listen to this" for me. Some, "meh, not their best" to be sure, but nothing I would call awful.
Currently heavily into Nightwish but their handling of the firings of their first two lead singers (out of three to date) feels a bit off so I can't really say they've done no wrong. Musically, though, I haven't hit anything I didn't like yet.