My 17 year old son loves his nook color. Has had it since last chrismas. He reads it all the time, even at cattle shows, no trouble with it so far. He has an ipod also, it is much nicer to read the larger screens. The Ipad would be tempting to me, but I let him choose.
Managing the account when the youngster needs to "borrow" your credit card number to get it started, takes a little comunication and monitoring. I've had no trouble and "nook cards" like Itunes cards, are widely available, to manage the amount spent.
I do not know how the kindle fire compares. Also, of course, make sure it doesn't go to school where all such toys seem to disapear, but I'm sure your are aware of that...
Mark