Personally I use AVR chips, and I love them. I am using an ATmega168 which is a great chip, nice amount of features and quick as well (20 MHz with an external crystal). Also, unlike PIC, they have a free compiler for C code. Either way you go you'll have a lot of users out there willing to help you... but if your son is new to programming, I imagine he is, then jumping into microcontroller programming isn't that great an idea. There are a few boards out there, Arduino is one, that are cheap and easy to use because of their librarys. I would recommend the Axon -- but it is most likely major overkill for someone who isn't going to be building anything too hardcore.