This subreddit likes FSX much more than X-Plane.
In short: X-Plane is still in active development, already 64bit, has a very active freeware and open source community but it is lacking in UI poliss, big airliners and the X-Plane ATC is crap.
FSX is not in active development, will never get a 64bit version but it is mature and has a very active payware community. You will get great scenery, weather engines and airplanes of all kinds for FSX in very high quality.
Also, if you want to fly helicopters you should get X-Plane.
Personally I chose X-Plane because I like helicopters.