[Riegerb]

From an aerodynamic efficiency and maneuverability standpoint, a traditional single rotor helicopter is far superior. However, the operational benefits, safety, and mechanical simplicity (way less expensive when they crash) of the multirotor configuration make it a very popular choice. The confluence of better battery technology and cheap/lightweight controllers has allowed for increased viabiliity. As the commercial drone industry matures and payload carrying missions become viable, I expect there to be a shift in popularity back to the single rotor configuration. For example, more than 30% of Japan's rice paddy fields are sprayed with Yamaha's single rotor drone [http://textually.org/drones/2013/06/032493.htm]. There is an exception here; the multirotor configuration is a more stable platform for shooting video.