I tend to like anything that's pared right back and sung acoustically. Quite a few on live lounge albums, but I can't think of a specific one from them. I might have to have a listen to some later.
The best cover versions take a song and make it something completely different: (Don't watch the video for too long!) (NSFW) Just 3 examples of how covers should be done...
Peter Tosh - Johnny B Goode (Official Video) - YouTube A rock classic given the Jamaica treatment. The sound of summer. Love it.