Or Comfortably Numb. Ooh, tricky choice. I mean, they're both perfect.
Shine On is obviously in the mix, just because 13 minutes of such compelling music can't be ignored, and it resonates with some great memories for me.
More left field choices for me are Not Now John and High Hopes. Won't say they're the best but hugely underrated masterpieces from the latter days of Floyd.