I really don't think it's fair to chose a single favorite song. It's much nicer to listen to the entire album and get the full experience all in one dose.

Wish You Were Here was the first actual CD I ever owned. Prior to that, I was stuck with dozens of cassettes. I half stole it from a family friend who loaned it to me after seeing how much I enjoyed the song Wish You Were Here (apparently he was amazed with me for not losing interest after all of the long, long introductory sounds before the songs) and I haven't ever gotten around to giving it back.

Years later, I went on to learn the alto sax parts in Shine on You Crazy Diamond and the guitar parts in Welcome to the Machine and Wish You Were Here (made a slide out of scrap metal and everything). They're the few songs I can actually play, but I'm proud for knowing awesome songs.