We have stayed at both, and are partial to AB. We loved building 14, very convient to the bus stop, food court, but very secluded feeling. Try to get a corner room, if you can.
At MB, we have stayed in Magnolia Terrace and Partiere Place. We preferred Partiere Place, again for the convenience. Just over the bridge from the main building, but still a feeling of being away from it all. Request a view of the main gardens in the back. The fountains are beautiful!~