It really depends on what you want.
If you want real scenery for cities, and I hear the ATC is amazing as well, buy MSFS2002.
If you want a more realistic flight model where the plane performs more realistically, buy X-Plane.
Those guys use X-Plane to develop their gyro plane thing, because the flight model is so good. Boeing buys X-Plane as do airlines and tons of experimental plane builders.
X-Plane more realistically simulates a plane flying through the air.