"UnWholly" by Neal Shusterman. Hands down, no competition, best book that I've reviewed here on Fiction and Frappe last month.
If you're interested in more books like this, check out "Lockdown: Escape from Furnace" by Alexander Gordon Smith. It's not exactly new fiction, so I didn't review it here, but I was reading it around the same time I read "UnWholly" and they are very similar -- and both are very good.
