A potential minefield of a question. Setting aside history and the capricious nature of feelings, I'm thinking instead about a recent idle conversation I had with someone. We asked each other what songs we'd want played at our funerals, and she said Queen Bitch by David Bowie. That response is one of the reasons why this individual is—and probably always will be—my favourite person.
I'd have to say Life on Mars, which starts fairly innocuously—especially when quoted in isolation from the rest of the lyrics and without the soaring musical accompaniment—but acts as a way of drawing you into strange, dream-like territory as the song unfolds.
It's a God awful small affair To the girl with the mousey hair