"Wide Awake". My predictions from just hearing the snippet coming true!
As for talk of how "Part Of Me"'s video didn't help it. First "POM" is terrible. Second it came way after the song's hype was over. This is a much different situation. Unless the video is cheap/live/from her movie, it will do wonders. People hear this song and honestly really love it, I know it happened to me. That's why it's doing so well.