One band that is, at least in my opinion the greatest cover song band of all time definately released the best cover song ever. I would have to say of course that the greatest cover song is from this band.
Of course their earliest and best cover song would be technically the best cover song ever.
So based on that it would be, I'm a king bee , rolling stones.
A cover song that is so great that in order to not be amazed by it's awesomeness , the listener probably does not comprehensibly understand music.