FWIW, I'm not sure there is a greatest all time song. Way too many great songs to rank one above the other.
A list seems more appropriate. To it, I would add numerous songs by Pink Floyd, the Stones, Jimi Hendrix, Carlos Santana, The Doors, Aerosmith, Little Richard, Styx, Lynryd Skynrd, Cream, The Band, BTO, Iron Maiden, Ozzy & Black Sabbath, Bob Seeger, Led Zepplin, Queen, GNR, the Eagles, Steppenwolf, Kansas, The Beatles, Journey, Metallica, Rush, The Who, Buddy Holley, The Kinks, Kiss, Boston. Did I leave anyone out?