I bought an Xbox one at launch. I use the Kinect for workouts, but I doubt many others do - Xbox fitness is closing, and the Kinect doesn't come with the one s.
I bought an S for my friend - it was half the price I (over)paid! It's significantly smaller, and better looking - even though it looks much the same (no, I can't work that out either!). It has a slightly better controller - it's textured so easier to grip, and has a 3.5" audio jack so you can use any headphones instead of the crappy one that came with my one. It doesn't come with one, but you can just use whatever you already have that is no longer compatible with your iPhone 7!
The only real advantage is 4K for bluray and some simple games (complex games are still lower resolution, you'll have to wait for the Scorpio for that), and HDR, if you bought a TV in the last year that has it.