I have the Nook because it was a Christmas present. Before that, I'd done some research and was torn between the two. Now that I have the Nook, I love it and, several Kindle owners have commented that they like their Kindle but really like the electronic keypad on the Nook vs. the button keypad on the kindle.
That said, there are a couple of things that have bothered me about Barnes & Noble, not the Nook, per se. The Nook was $250 last Fall but, six months later, is now $150. That irks me even though I know its all marketing.
The biggest gripe I have is they advertised that most books will be less than $10 and they were, for a short time. Now, the most popular authors, who were sold at $9.99 in January, are now at $12 and up. I knew that this would eventually happen, once B&N built a market, but this is a BIG jump in price, more so than I would expect in the price of paperbacks. Guess the same thing could/can happen at Amazon.com but it still irks me.
Bottom line, I love the Nook and the whole idea of an eReader because I travel a lot and, being a prolific reader, I've literally run out of space to store books. Hope your son enjoys his present!