The Index is better overall, better headset, better screen, and you can use Base Stations from the original Vive - although the base stations that use SteamVR 2.0 tracking are much better.
The Rift S is great for a out-of-the-box experience, there is only the Guardian setup (a virtual barrier you draw with a controller to give you a area to play in) to do. There are no base stations to buy and setup, the Rift S uses inside out tracking. You literally buy the Rift S and start, thats it. The Touch Controllers are slightly better than Valve's controllers, although most of the reviews are personal preference. The Rift S controllers, the same as the Quest, do have major flaws to them. In the inside part of the tracking plastic ring there are joins which are part of glued plastic parts glued to the ring - if you strike a controller on a wall, TV, or drop them on hard floors, they can easily break on these joins/seams so you are left with a cracked controller ring.
Drivers are good, Oculus did have some teething problems with their xmas v12 driver roll out. But one major thing that might put you off is the fact that Oculus is owned by Facebook. In their newer drivers, you are forced to have a Facebook account if you want to use VR social features such as Oculus Home. For the moment, you can ignore this and use the Rift S without Home and never see a Facebook account. I just worry Facebook will integrate themselves more and more into the drivers, and what makes this worse is that you cannot choose your drivers and headset firmware, you have to have the latest or you cannot use the Rift. There is a workaround, such as blocking Oculus servers in your Host file, but then you cannot use Oculus store features, or buy games. So if Facebook bothers you then you might want to look at a different headset. It does bother me as I don't use social media, especially Facebook, so for now I stay away from Home, and keep a keen eye on the drivers.
One last thing, there is no hardware IPD slider, only a software IPD setting. If your eyes are between somewhere around 60 - 72 approx, then you will be good to go. But, if your eyes are further apart than 72, or closer together than around 58 or less, then I would look at the Index.
