What, like most demanding/nicest looking? Or most entertaining and fun? I believe the DX12 "Elemental" demo works with the Oculus dev units. I haven't gotten around to testing it but this thread has reminded me to give it a run after work.

As far as most entertaining, that'll probably depend on what you're looking for and what your platform is. I've only got a Rift DK2 so I don't know about GearVR or Cardboard or Vive, etc.