Rift S. There is also the Oculus Quest which is standalone but can now be connected to the computer using a USB cable and what Oculus is calling Oculus Link . However it is still beta and there seams to be some connectivity issues with SteamVR as well as image quality issues since using a single USB cable requires some serious compression tricks.
Here is how Link works.
https://developer.oculus.com/blog/h...the-architecture-pipeline-and-aadt-explained/
Short answer everything outside of the center of the image where you will be looking is seriously compressed.
The other difference between the two is that the Rift S uses a LCD screen which does provide slightly higher refresh rate 80hz as well as what some people say is less "screen door" effect (mean that you can see the individual pixels) compared to the Quest which is OLED but does provide better colors and blacks.
Finally the Oculus Quest does have a IPD adjustment, this adjusts the distance of the lenses for people with eyes further or closer together then the "average" which Oculus for the Rift S has determined to be 63.5mm. I would suggest if your IPD is more then a few mm outside of the 63.5 then a headset with an IPD adjustment like the Quest or Vive Cosmos should be considered.
Here is a guide on how to very accurately measure IPD
http://doc-ok.org/?p=898
Finally make sure your computer is capable of running the required refresh rates as droppping below the normal refresh rate of the VR headsets will cause motion sickness and discomfort.
My thoughts would be if you have the money and really want to invest the HTC Vive or Valve Index would be the top choices. Although Ive been reading that the Index is having some issues with faulty controllers.