Hi,
I can tell you about our experience with our son playing AAU basketball. It was a mixed experience - very expensive and in the end probably not worth it in terms of a basketball career - but we all made good friends and had a lot of fun.
I think the real key is the coaching- how good are the coaches, how fair, how well do they know the game - do they have favorite players, kids of their own on the team? Do they treat this as a learning, growing experience or win at all costs?
Our son played for 2 years - the first year they qualified for Nationals and played in Cocoa Beach. It was a blast but they're kids (10 and 11) and they enjoy the moment. When they lost their last game they were sad about 5 minutes and ended up playing in the ocean in full uniform!
Now a couple years later our son is barely playing basketball - he opted only for rec this past season and had a pretty awful team. He stuck it out to his credit and at least had one good game, their last. His passion is now theatre which may take him to a half day magnet school not allowing him time to play basketball in high school.
On the other hand his sister (who for years said she hated basketball) has turned into a pretty good player. It's soooo tempting to find an AAU team for her but we've decided to lay off and see what happens. Basketball just ended and soon she'll start soccer. Next year she can try out for town travel and the middle school team.
My best advice - ask a lot of questions, watch the coaches if you can. It's such a fine line between AAU teams being money making ventures where they will take almost anyone who comes with a parent willing to pay - to teams that are too competitive.
Good luck.