Definitely the Fallen. Their hierarchy is very interesting and really ties in to their culture. Very conflicted, but determined. As far as the Kell goes he and the Archon have an arrangement. The Archon hears the needs of the House, gets updates from the Prime Servitor about where to go, and generally keeps track of culture and religion. The Kell keeps 'em in-line and oversees military operations and in general finds the needs reported by the Archon and decides how to get where the PS dictates. What's most interesting is that while they're given some serious leg room they are incredibly bound by the Servitors as they supply the Ether necessary for survival. Much of this is elaborated in The Arena's Armor flavor text. Most excellent read.