Your vote for greatest (covers) album

I don't know of any album sloppier than Sid Sings, but I, too, have enjoyed it a lot.
Yes, the Motorhead covers album is good, and I also liked Guns N' Roses' Spaghetti Incident and Metallica's Garage Days Revisited; both had a couple low points, but the highlights more than made up for it.In that same era, Slayer put out the note-worthy Undisputed Attitude, which had its moments and was mind-blowingly fast, even for Slayer.
My all-time favorite cover album, though, has to go to The Walkabouts' Satisfied Mind.  It is a phenomenal album by any measure.

Bryan Ferry's These Foolish Things (1973). Covers of the Beatles, Stones, Dylan ... I have the CD on order!

+1 mammothguy54! Bowie's Pinups is great! I forgot about it! Thanks for the reminder!

Once a week I listen to the version from Nina Hagen and Apocalyptica of Rammsteins "Seemann" - it is amazing.

1-Jethro Tull “Thick as a brick” not just for the music talents but also one of the best produced albums ever.
2- Doors “ LA Women”
3- Pink Floyd. “The Wall”
4- AC/DC “Power Age”