It really depends what you want.
If you want to use Microsoft FSX in VR, than you want the "FlyInside FSX" download. If you have a headset from Oculus (Oculus Rift) you want the one for Oculus, otherwise the SteamVR one. Which VR headset do you have?
We also have our new simulator you can read more about here:
https://flyinside-fsx.com/Home/Sim. It's in beta so it isn't feature complete yet, but it has a really nice VR experience.
Thanks,
Dan