We've had topics such as 'Theme songs' and 'What are you listening to right now?', and i'm sure we've also had a topic much alike this one, but i felt the need to make one anyway. It's pretty simple, what's your favorite song?
Tastes change over time, you may find a new favorite song or maybe you have several favorite songs, maybe you don't have one, or don't know of one. It doesn't matter if it's a song you've fallen in love with temporarily, a song that you go back and forth with, or one of many favorites, make whatever post suits you, as long as it is, in some way, a favorite of yours. Simple as that.
Mine would probably have to be Beethovens piano sonata no. 14, Moonlight Sonata that is.