MS: Flight Simulator X was always my choice. I spend a good amount of money on addons etc. + there is tonnes of free mods out there.
I think the top end flightSim now is still Prepar3D.
Wikipedia wrote:
Lockheed Martin Prepar3D
In 2009 Lockheed Martin announced that they had negotiated with Microsoft to purchase the intellectual property (including source code) for the Microsoft ESP (Enterprise Simulation Platform) product. Microsoft ESP is the commercial-use version of "Flight Simulator X SP2". On May 17, 2010, Lockheed announced that the new product based upon the ESP source code would be called Lockheed Martin Prepar3D. Lockheed hired members of the original ACES Studio team to continue development of the product. Version 1.1 was released in April 2011, with a retail license cost of US$499. A developer license is also available for a monthly fee of US$9.95. In March 2012, along with the release of version 1.3, the pricing strategy was revised. The Professional edition is now available for US$199, with an Academic License available for US$59.95.
The real money sink is going to be peripherals.
Need a good joystick. (preferably a flight yoke)
Throttle quadrant
Ruder pedals
TrackIR is a must have (or Oculus/HTC-Vive)
for good reading material get a subscription to PCpilot