I guess Ember's my favorite. Partly because she likes books and is inquisitive and such like I am, and partly just because she's the only one I really have any sense of. None of the characters really stand out at this point, but that's normal. Characters that "really stand out" are ones like Adrian Monk, Hannibal Lector, Sheldon Cooper, et cetera. The crazy/disfunctional ones. I find them to be very entertaining. Flaws make the character, and with more normal characters, you don't get to see their flaws right away.
Takes me a while to get to know characters, though, and I have a feeling we'll get to know them better now that the plot's really picked up. See their reactions in the aftermath of the escape attempt. (I'm having some trouble telling Cole and Bernin apart due to physical similarities. Maybe one could fall into a vat of permanent red fur dye or something?)