If you are not that great at computers or do not want as great of a installation or computer challenge, than Microsoft Flight Simulator X (FSX) is easier to install and operate. However, it is limited in the flexibility in screens, views and modifying the aircraft to meet your needs. However, adding additional aircraft can be the biggest challenge of all. There are not as many additional aircraft that can be added to FSX.
Laminar Flow X-Plane does take a little more effort and understanding to set it up, get going and operating, however, it provides total flexibility in the program plus modifying the aircraft, aircraft performance and the instrument panel. There are numerous additional aircraft that can be added and typically they are easy to add plus modify.
Overall, you should look at the available aircraft you want to use before deciding on which flight simulator to use.
Google Flight Simulator is pretty easy to install and use. You simply install google earth and the flight simulator is part of the Google earth installation. As discussed earlier, Google earth flight simulator only has two airplanes and is best for looking at the the actual terrain but not as useful for learning to fly an aircraft.