Henry , The most efficient cities can be deceiving. Apartment living like huge high rises in NYC can be very efficient since they share the same interior walls as their neighbors. While detached homes and bigger homes use a lot more energy. There needs to be a very detailed measure of how energy efficient each home of similar size is. The local weather would also need to be considered as California has very moderate temperatures while Northern states are very cold in winter.  the deta T, Temperature differences should be included.