There is no "The greatest" for me, there are many tunes with powerful messages, some of which I took for granted. What I mean is I was just enamored with the music itself, I never really paid attention to what was actually being SAID. When I was younger, there could have been songs with lyrics like: "Anybody who feels the need to sing a long with this song is a complete idiot" and I probably would have happily sang along with it. Now I pay attention as much as I can to lyrics and I realize The Beatles, Dylan, Rolling Stones, and The Doors are powerful musicians. There are others but those bands/artists are pretty damn good.