Really? Pretty weird reason to prefer playing games because of the OS. The OS you won't see when playing the game... Unless you mean for the moments you go back to the OS at times.
Personally I vastly prefer the PS4 OS atm. It seems faster for sure. X1 is winning for features and customisation though, but they need tweaking and speed needs improving for sure, but I do see the potential of the X1 OS.
There are plenty of reasons why an OS can make you prefer playing games on one machine over another.
I can be watching TV and still receive a game invite from friends, and start playing due to that.
I can actually see when friends come online, because it bothers to tell me.
Twitch broadcasts don't embed the damn UI into the stream.
Can opt for Skype calls instead of party chat, so I can talk to my brothers even when they're not on their consoles (one doesn't even own an Xbox One yet).
Can snap various apps to the side, so if I'm waiting for a show to start, I can still be playing meanwhile.
Recording shit actually works reliably.
I bought my PS4 with the assumption that I'd be purchasing console multiplats (that don't have a PC version) for it due to the superior specs. These days though, I'm hesitant to do so, as the Xbox has integrated itself so well in my setup, that playing anything on the PS4 feel extremely segregated from everything else I do. Now unless the port is a disaster (and 900p vs 1080p is not a disaster to me) on Xbox One, I'm probably going to end up buying that version instead.