Willie/Gateway is very pilot-mill oriented (I instruct there). You have ATP and CGCC/UND for flight training on that field. I wouldn't recommend an intro flight there, that's not what real flying is like. I think Chandler would be a much better and more authentic experience for a discovery flight. My best friend is an instructor at Chandler Air Service, lots of experienced instructors, nice planes, and they know what they're doing.
However, if your son is interested in the ASU/ATP 1,000 hour 141 program it might be worth it to stop by Gateway as well.