Due to its long history of development it has some of the most well received third party aircraft add-ons, but be warned, these will cost more than the sim itself.
If you want a video game, you should get the new MSFS. If you want something more realistic you should get P3D + third party aircraft for airliners or XPlane for GA aircraft (+ setup ortho scenery for XPlane), but much of the ecosystem is slowly releasing MSFS ports too.
I am a little worried for what will happen to hobbyist flight sims after MSFS though. A large part of its appeal is the bing maps powered streaming of good terrain and other map features, and I suspect Microsoft won't maintain that forever. If they lose interest for a similar length as between FSX and Microsoft Flight or between Microsoft Flight and MSFS, that could be a bad time for the flight sim world if they've gotten too used to MSFS.
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If you do get into the P3D third party ecosystem, be warned that many of the developers are older hobbyists turned devs which have been in their own universe and so can have weird ideas from time to time. Like a support system that is a public forum where you must manually sign your real name at the end of each post or get banned (PMDG), or uploading the chrome username/password DB of suspected hackers based on a check for username (FlightSimLabs).