Good: Anyone else's cover of any Dylan song - except maybe "Idiot Wind" and a few like that that would sound stupid if they were sung instead of shrieked.

Good: Emmylou's cover of anything, by anyone, up until 4 or 5 years ago.

Classic: Haggard and Jones' cover of Willy's "Yesterday's Wine," with howls.

Awful: Dylan's rendition of "Jim Jones" (aka "Botany Bay.") Compare Ian Robb. Which reminds me:

Good: Finestkind's cover of anything at all.