The Moment I Said It by Imogen Heap.
I love this song.
It's so wonderfully ethereal, beautiful, and a bit haunting.
Of course I see Mia Michael's choreography with this, but I also see it being a boy meets girl situation, and ensuing heartbreak. It goes through the whole spectrum of a relationship from beginning to end.
This song is best paired with a situation where there is about to be an incredibly beautiful, or tragic moment. How many songs can have that kind of versatility? :)