Unless you've tried X-Plane 9, then I suggest you try it before comparing them. Neither is, on a whole, 'better', it comes down to your individual tastes & preferances. For example, many I know swear by X-Plane, because the flight dynamics in, particularly abnormal situations, are light years ahead of MSFS. I can give very significant examples if you wish.
Other people, on the other hand, love fs9/x because the graphics, immersion factor, cockpits, avionics, atc, multiplayer, missions, modifications, etc make it so much more worth while.
If you want to know what it's like, then download the demo.
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Flight Simulator and other chat