HI Gretel-
We stayed at ASMu for 3 nights before transferring to the BC, I found the room to be clean and servicable, but that is it, as with all things Disney, you get what you pay for. I would definately not choose ASSports because I've heard it can be loud and many groups of sportsteams and cheerleaders stay there. My friend stayed at ASMo, and liked it. The transportation from all the AS was excellent, buses running constantly and very effieciently, the only drag is the AS bustops are the furthest away from the entrance at every park, so bring good walking shoes. Also there is quite a distance from most of the rooms and the bus stops and food courts. Considering your childrens ages, I would suggest ASMo if possible. The theming will be familiar, the ASMu was just instrument/ musical theme, cute but not tons of kid appeal. Have fun!