I'm an audio design engineer, and the best advice I can offer is that there are two elements to the best choice for your son, audio quality (of course) and comfort. The best way to choose a good headset is to go to one of the larger stores in your area and listen to them. Take your son with you. He's the one who has to be comfortable with the physical model, and he'll know you're into getting phones he'll really enjoy.
Once you have a few makes and models in mind, it's easier to shop online for the best prices. Many stores even match online prices so you may be able to find the phones you like at a local store for close to the same pices you find online.
Hope that helps.
