I'd say the most popular Pink Floyd song is... well, I can't tell. The top three are Another Brick in the Wall, Comfortably Numb, and Money. Money here gets a lot of airplay while other songs languish. Personally, it's very, VERY hard to pick my favorite Floyd Album, more or less song! I'd have to say that the Album "Wish you were Here" is probably my top favorite, as everything on it is really awesome. As for top song, it's just too hard. Everything on Animals, WYWH, DSOTM, The Wall, Momentary Lapse of Reason, it's all good. I also like Meddle and the Division Bell.
While I believe most songs here were picked due to their AIRPLAY, I do agree they are all some of the best Floyd has produced. That being said, I feel most of their best never has even be played of mainstream radio for the masses to hear much less judge! The following songs would be my list of their best work, given the enire work of pink floyd.......One of these days, Gunners Dream, Shine on you Crazy Diamond part 1 or 2, it doesn't matter, Saucer Full of Secrets, Careful with that Axe Eugene, Welcome to the Machine, Comfortably Numb, Hey You, Pig on Wings, Time, Dogs of War, One Slip, Money, The gGreat Gig in the Sky to name a few!