Like others have said it's tough narrowing down a specific all-time favorite song, so I'm picking one that has been done in many renditions by many different artists. No one variation is my fav, I just love the song.
"Feeling Good"
Cy Grant feat. Bill LeSage performing the original recording, from The Roar of the Greasepaint - the Smell of the Crowd
Nina Simone Easily the most well-known, some of y'all might recognize this heavily-sampled version from
How I Feel by Wax Tailor, as well as a number of soundtracks, ads or other dubstep/house tracks
John Coltrane
Black Cat Bones
Traffic
Muse with a pretty cool music video
Michael Buble with a fuckin' awesome video
Pussycat Dolls
Joe Bonamassa
My Brightest Diamond a great version not many have heard, well worth a listen.
Anyway these are just a few of the many renditions, it's been sung by probably hundreds of artists. Sick song.