Well, I'd have to say it was "Paranoid" - Supposedly by Black Sabbath, but only if Ozzy Osborne is singing it!
It was what gave my husband the courage to ask me out on our first date - he saw me walking back to work with the single (this was in the olden days when music came on round black vinyl things with grooves in). He asked what it was, & if I was into Rock Music. I said "Don't know anything about Rock, I just like the song"
Ozzy Osborne had just left Black Sabbath (and still had blonde hair!) and he was playing in our town so he asked me to the gig for a dare - the rest is history!

Not many people can say their first date was an Ozzy Osborne concert but it was a great night and my ears ached for days.......

I also especially like the album "The Wall" by Pink Floyd (which I saw in London in the eighties and it blew me away!). You can't really pick one track because you have to listen to it all from start to finish to appreciate it.