There is no best building system! All systems have their own pros and cons. They best system for one person may not be the best system for another. A good energy consultant will identify what is important to you and devise the best solution around your demands. Some of the criteria people consider is cost, efficiency, speed of construction, user friendliness, fuel preference, location, thermal mass, wall type, insulation type, occupancy, temperature, living habits, ventilation, type of windows, type of heating, water efficiency, renewable energy, environmental impact etc.