I actually prefer XP10 over FSX.
XP10 has some real nice additions graphics wise, and it always felt more like flying to me than FSX. For some reason, most of the aircraft in FSX, payware and freeware (that I have tried) just feel like they fly on rails and that they aren't "moving through the sky". It just feels stale at times. Flying at night is also really lacking in FSX.
FSX definitely has a lot going for it with the AI and variety of add-ons (including both aircraft anf locales) with huge 3rd party support, but overall, it just feels "off" to me. Almost like the "feeling of flight" was an afterthought in favor of "How much can we cram in this product?". XP10 is $80, I imagine, because the (Full) scenery install is over 50GB and includes a LOT of terrain out-of-the-box for the world.
Both are great products. It just really depends on what you are looking for.
I do love XP10 + The JRollon CRJ though.