From a personal point of view, this is a very tough battle as it pits two classic songs by two of my favourite bands against one another, but I will go for Time. I absolutely love Immigrant Song and think it is a perfect compact hard rock song, and would vote for it in most contests, but I have always thought that Time is the best song on The Dark Side Of The Moon, and if I discount the album-dominating epics Shine On You Crazy Diamond and Echoes it is only really rivalled by Comfortably Numb for the title of my favourite Pink Floyd song.