>>270263782
You are totally dependent on one guy's jank software if you want to play good game (Oculus exclusives)
Index has better FoV with less SDE but less stereo overlap, so things are less 3D looking. It also has some bad internal reflections that can get detracting, while the Rift-S lenses feel nonexistent they are so clear and distortion free. [spoiler]Assuming you fit the IPD range [/spoiler] 
Index is torture if you are round headed. You will likely find the S more comfortable over all