My Favourite is definitely the Tower. I don't know, it just has a very mystifying and catchy sound to me. I love the clouds that scroll by really fast and the monks floating in the background. It's just such a weird place.
I also love the Dead Pool and The Armory. Those two are alot slower than the other tracks and come off as darker and more moody. Dead Pool in particular is a very creepy song, especially the end of the track when you finish off your opponent and Watch Insidious Chapter 3 Online.