This review will be focused on my experience with the new Oculus Quest and Oculus Rift S, and will not focus on the specific specs of both of the headsets.
The Quest has a similar form factor to the previous Rift while the Oculus Rift S features much more padding and a twist to tighten mechanism to achieve maximum comfort. I found the Quest felt a little heavy towards the bottom of my face, and wasn't as comfortable to wear for a long period of time. The S is the much more comfortable experience and really fits nicely onto my head. The twist mechanism also provides greater controller over the tightness. This also allows for better resolution since the screen remains more optimally located. An advantage of the Quest is that it does not have the tether that the Oculus Rift S has.
The tracking capability of both headsets is greatly improved with the cameras mounted all over the headset instead of using the towers that the previous Oculus Rift used. One of the cooler experiences of putting on the headset for the first time is the passthrough view that you get when setting up the Guardian System. One major difference between the Quest and S for tracking is that the Quest is missing the front facing cameras that the S has at the bottom of the front. What this results in is on the Quest when you hold your hands close to your face, you lose tracking in the front since the headset can't see the controllers. This only happened to me a couple times while playing Beat Saber, but I've heard that boxing games suffer for setting up for blocking.
Both the Quest and the S share the same controllers. They are very similar to the previous controllers with the most noticeable difference being the circle forming in front of the users hands instead of behind. My first experience with the controllers felt a little weird with the weight distribution no longer being heavily on the palm and more evenly distributed through the controller. The battery slot also had some slipping in games with a lot of movement such as beat saber.
Both the Quest and the S boast spectacular visuals. As far as quality goes, the S definitely is able to render much higher graphics through use of your computers GPU. This was most noticeable while playing Robo Recall. The Quest still has great quality and performance was consistent while playing Beat Saber and Vader Immortal. I did notice a few times some lag while playing Robo Recall on the S, but I'm not sure if that was due to my computer running multiple things at once (I have a 1070). The S has a much larger selection of games with SteamVR and also the Oculus Rift store itself. Since the Quest is the first mobile VR experience to utilize touch controllers, there is a smaller selection of content available.
Both headsets are a great improvement of their previous generations. The Quest brings great mobile VR with its design, and touch controllers. If you are just getting started with VR, I recommend getting a Quest as you don't need a high powered PC to run it. If you have a high powered PC already, the S might be the right option for you as there is already a large store full of content, and the graphics are much higher.
Thank you for your time reading!