depends on your computer....
Im in the process of building a computer for Flight Simulator X but ive heard even a really high end pc wont be able to play it to its full capabilities.
But the graphics are awesome....
Then their is Flight Simulator 2004...
Which would run awesome on a mid end system.
Their are more downloadable aircraft etc etc for FS2004.
But for me im going for FSX as im building a new computer anyway