If you want a more lively experience, fly UA/DL/AS/AC. Prior to US Airways moving out of A, every single gate was being used. Now without them, it's cleared 3 gates, but even so, there aren't very many amenities at those gates. Lines can be long at the checkpoint and crowds regularly block the narrow terminal hallways. STL sure has heck doesn't seem "quiet" when you're at the A gates.

Even though AA isn't what it used to be at STL, consider yourself lucky that you don't have to deal with the throngs of people at the A gates on a typical afternoon.