Sympathy for the Devil. Loved it the first time I ever heard it, and still do.
That's why I could never answer the op's question. So many different songs have various emotional meanings to me across a lot of genres, it would be impossible to pick one. It would take a big effort to get it under a top 50.I rather suspect that many of the selections that folk make for a thread like this will be more lead by emotions than a feeling of what would constitute the best number one. I think in reality there cannot be a 'best' because the music covers so many genres. That said, I'm enjoying the selections, whatever the reasons for them.