Buy the Xbox One if That's Where All Your Friends Are
If your friends all play on Xbox One, you should strongly consider buying the Xbox One instead of a PS4.
We're seeing cross platform play with more games, so this isn't as much of a reason as it used to be, but there are still some games that you can only play with or against people on the same console.
I've built up a long list of Xbox Live friends who I play against and that is the reason I buy most of my games on the Xbox One, even though I own a PS4 as well.
If your squad of friends is on the Xbox One, it's a big reason to buy an Xbox instead of a PS4.