I fiddled a bit with an X1 (also did the PS4 HDMI input thing).
At launch, the X1 is better equipped than the PS4, but is laggy, and glitchy. FM5 played like a dream but there were several nuances that threw me off because of the hardware. The first problem is voice recognition, I live in a Spanish speaking country and the thing sucks at taking Spanish commands recognitions, it did better when it was set to English, but once we started using it on Spanish it wouldn't recognize commands, or simply misinterpreted them.
Everything is done with the "xbox, do this/that", and it does in the way when you are talking about the xbox, people who were on the demo unit were pretty confused because they said "xbox this, xbox that" and it became a mess because it would switch out the game, launch explorer, launch skype, open guides, open notifications. The tech is amazing, but is not ... practical, neither reasonable, PS4 have limited voice commands, but the whole interface fluid better without the eye thing, or the voice recognition thing.
Software wise, the X1 has better downright better exclusive games (dead rising and FM5 were awesome), but it has more things that get in the way of gameplay like notifications and such. I found no point to the whole integrated TV thing either, is cool to have guides and all, but is something set-up boxes already do (in this case Direct TV) and is rather blotting the whole game experience thing. There are already smart TVs that have similar but better functionality, and the price for the thing locally is just outrageous (650 USD because kinect).
I can see that is designed for the American market, I don't regret getting the PS4 instead of this, but is a total shame that the X1 has better software for it (at least at launch).
War thunder is due to the 29th, when I would have something to play on PS4 (might get KZ shadowfall once I get the yearly PSN+), however as of now I would have much more fun with the X1, even if it has a more problematic UI and hardware.