My xbone gets the most use out of my gaming devices. Partially because of the games, but also because it actually makes a surprisingly good streaming hub also as a window 10 OS it in theory could get apps and other neat things from windows.
I use Netflix, Amazon, Hulu, and various other premium channel apps (HBO, CW, etc). While the ps4 does many of those, I have to open each app and hunt for the shows I want. the xbone lets me do a search via voice and then asks what app to open the show in. Way more convenient. The xbox also does live TV and has tv guide and all that stuff. Basically, it replaces the features of a smart TV+
Game specific stuff:
Exclusive wise, Sony still has an edge, but it's pretty small. That's when I typically use my ps4. Quantum Break is good, but short. Tomb Raider is amazing, but will likely be coming to PS4 in the next year. I'm also a bit a halo fanboy, so that helps.
Both consoles give free games each month if you have their premium account thing.
Xbox one however has backwards compatibility with a bunch of 360 games, so I'm using that a lot as well.
You can also use the xbox as a miracast receiver, which I use fairly often and works well. Granted you can get a standalone receiver for WAY cheaper, so don't buy it for that.
I loved xbox fitness, but they are killing it... Still a bit frustrated at that.
Xbox can be targeted with universal windows app, since it's a windows 10 machine at the core. So the preview program has just started getting actual windows 10 apps on it. Which I'm very curious if that will be awesome or horrible; to early to tell.