My guess is the Zutons' "Valerie" although she liked a number of 60s girl group songs as well as "'Round Midnight" in her younger years. But has Amy ever indicated what song of her own she liked best? If I had to guess, it might be TDOTO or perhaps "Just Friends" (because of an emotional rendering on a YT video where she repeats "just friends" several times at the end of the song. I can't find it right now). Has Amy ever indicated what song of her own she liked best? I definitely don't think it was "Rehab". It's not a bad song, but I think she was sick and tired of singing it everywhere.
EDIT: Sorry. The song was Donny Hathaway's "We're Still Friends", not "Just Friends". A great performance BTW.
http://www.dailymoti...friends-e_music