If you have a PS4 already, get the PSVR. If you have a PC, get the Index or Rift S. If you have neither, get the Quest.

PSVR has some exclusives, like Blood & Truth, and Firewall Zero Hour. But it has really garbage tracking, and no joysticks on the controllers, and if you want to play Firewall, you gotta shell out extra money on the Aim controller, and it has the lowest resolution compared to the Quest or Rift S. Only get the PSVR if you have a PS4.

The Index and Rift S must be plugged into a PC if you want to use them. They have much better tracking, and apart from plugging them into your PC, you can freely move around compared to PSVR. Get the Index or Rift S if you have a PC.

The Quest is the heaviest out of all of these, since everything is built in, you can play games like Beatsaber and Superhot, but not graphic intense games like No Man's Sky or Skyrim VR. I'm pretty sure you can plug it into your computer, but if you can, there's no point in getting the Quest when you can buy something lighter. Get the Quest if you don't have a PS4 or PC