Best version of Flight simulator.......?

Tweet

Presently i am playing Microsoft Flight Simulator 2004 and now planning to get X-Plane 7 Because of less system specs instead of latest version 9.I also have downloaded Flight Gear which is free and Open Source but its not Working at my PC don't know why.... While my question remains there that which Flight Simulator Version is the best one between i have known or any other i have not mentioned.....!