I recently got a PS4 Pro as a present and will likely trade my old one in for an Xbox One S.
I actually have so-so nterest in the One library but Microsoft does have a great backwards compatability feature. I intend to use the One as a mediahub for my old (720p, suits the sub-HD One S) television and to check out some of the following titles:
-Witcher 2
-Morrowind
-Fable and Fable 2 (the anniversary stuff)
-Gears 2 and 3
-Jade Empire
-Splinter Cell Chaos Theory and Blacklist
-Alan Wake
And perhaps some classics I enjoyed as a kid on the PS2.
As for the One, maybe I'll try
-Sunset Overdrive
-Forza Horizon 2
-Gears 5
-Quantum Break
-Rare Replay
Don't know other games from the top of my head. I don't like Halo and don't plan on going online for MP stuff.
Also, my gaming laptop died and I don't think I will return to gaming pc's for the coming years. I have extremely bad luck with them and on a pc there is too much distraction for me to dedicate time to gaming. And on PC I always end up tinkering for way too long. Which is odd because on consoles I don't care that much when a game isn't well optimised. Anyways, the Xbox serves well to try some of these classics for cheap. But yes, I own quite a bit of these on steam already