My favorite album is Parliament's "Mothership Connection" from 1975. My favorite song of it is hard to pick. Maybe it's "Supergroovalisticprosifunkstication", but then again it might also be "Mothership Connection (Star child)" or "Give up the funk (tear the roof off the sucker)" or maybe "Night of the thumpasorus people". It's really hard to say, as it's my favorite album of all time as I said. I can say which is the least good on it though: "Unfunky ufo", although this is still cool!
Any of the mentioned songs wouldn't even get into my top 100 I think. My favorite song is clearly Gershwin's "Summertime" and my favorite version is the one done by Ray Conniff, his orchestra and chorus.