It is, quite possibly, the only question in existence to which every answer given sounds ludicrous.
Even queries as massive in scope as “Who was the best person to ever live?” beget potential responses agreeable to most who hear them; an answer of “Mother Teresa” will elicit a thoughtful nod as a fair answer, for instance. Asking “Who was the worst person to ever exist?” not only has plausible answers, it even has a de-facto correct one: Adolph Hitler. Or, possibly, Nicki Minaj.
But offer your two cents on what the Best Song Ever is, and you will surely be met with an instantaneous and vitriolic “Oh, that is fucking dumb. No way. How could you even think that?” You can go with The Beatles, Stones, Dylan, or Oingo Boingo, and sure as the sun will rise you will have picked the wrong one to crown as the best.