I think at this early point I would say Nafaryus. I was worried on account of his name that he would be a very boring villain, but I was pleasantly surprised that JP actually wrote him as a multifaceted character who has a deep inner love for music that he has repressed and pushed down out of a desire for control. If JP ever brings us back to this world, I'd like to learn more about Nafaryus, how he went from the kid with the iPod to the power hungry dictator, and then what he did after his somewhat redemptive story arc. I honestly think that his family tensions are pretty interesting as well, since he has an abiding love for Faythe that is the thing which ultimately helps him overcome his obsession with power.
Plus, "Remember Bug?" is just a great moment. I'm not going to praise the story of this concept as a modern literary classic or anything, but that twist is awesome and the line is really cool, because is totally switches our perception of Nafaryus and makes us see this kid running around the palace with his iPod. I think that's probably the most clever part of the actual storyline of The Astonishing.