I guess if your list is long enough, any song can be one of the greatest, but it starts to feel strained past 25th (eg "what's the 38th greatest meal you've ever had?"), and I could list 50 greater rock songs (than "Brown Sugar") just from the Beatles, David Bowie, Led Zeppelin, Pink Floyd, the Rolling Stones, Queen, the Kinks, the Who, Jimi Hendrix, Cream, and Clapton off the top of my head.