Hi,
I live in Prince Georges County. I work in downtown DC near the Whitehouse. I drive to the Metro station and read the paper and get to work on time 95% of the time. The Metro system is better than its reputation, especially if you do not need to ride the Red line during rush hour.
I recommend the Greenbelt area in PG County. Your son would go to Roosevelt High, which is the best public school in the county. There are apartments in the area as well as housing. If you find a place in Old Greenbelt, you will be really near the Green line of the Metro. I know many people in the Old Greenbelt neighborhood. They are nice, friendly, intelligent people. A little on the hippie side but most of them are professionals.
Please contact me if you have any questions.