I live in the downtown Chicago area. My Apple store of choice is on Michigan Avenue. It's a beautiful store. The location is very typical of Apple's larger flagship stores. Consistently I've found the staff to be friendly and knowledgeable. I come at them with some pretty technical questions. Most of the staff can answer my questions. Even when there's a staff member that can't they quickly usher the support of another team member or politely refer me to the Genius Bar. It never bothers me if someone doesn't know the answer as long as I'm directed to how to get it. The staff has a great laid back appraoch that I think really works well with customers. Not all the staff receive an A, but most of the time their consistent.
Last week I was out in the Chicago suburbs. Apple has three Chicago suburban stores with representation at each major mall. I talked with two or three of the staff at the store and couldn't believe what a difference there was between this store and the downtown location. I observed staff not focusing on customers, freely talking about personal topics in front of the customer and having an ambivalent attitude. You might find this at non Apple stores, but compared to the location downtown it really stood out. Good thing I'm close to the downtown store.