If you just wanna play some gat dang games
Both the PS4 and the Xbox One are fantastic at playing games. A whole hell of a lot better than your old 360 or PS3, and probably better than your PC if you don't have a real, tricked out gaming rig. Moreover, since the Xbox One and the PS4 share a x86 architecture this time around, they are more alike than they've ever been.
But the PS4 has one big advantage over the Xbox One if literally all you care about is bleep bloop and pew pew. At $400, the PS4 comes in a hundred bucks cheaper than its Microsoft competitor. Sure, you miss out on a few Kinect bells and whistles, but none that are central to the gaming experience. The PS4's guts can churn out a 1080p stunner just as good as any Xbox One, and sometimes even better. COD: Ghosts on runs at upscaled 720p on the Xbox One, while on the PS4 it's pure, native 1080p.
You should buy: PS4
If you want the whole package
Alternatively, maybe a few hundred dollars is more than you want to pay just to play some games. Maybe you need a little more out of that investment. While the Xbox One is $100 more than the PS4, it also adds at least that much value in futuristic weirdness and set-top boxitude.
If you've got cable, the Xbox One can reinvent that horrible mess of a channel guide you have, and boil it down to just the ones you actually watch, while throwing in your favorites from Netflix or Hulu Plus or whatever else you like. And while the Xbox One's voice commands and Kinect-identification aren't perfect, they are there, and they're fantastically useful when they're working. And that's on top of it being a perfectly functional next-gen console with all the game fixins you could hope for. Having to shell out for Xbox Live Gold to get streaming is a drag, but that's the (stupid) price you pay for getting everything in one place.
You should buy: Xbox One
If you need something right now
The launch lineups for the PS4 and the Xbox One aren't exactly mind-blowing. Launch lineups for consoles rarely are. As time goes on and developers learn more and more tricks for really squeezing every ounce of juice out of these things, and putting out games that can really make your jaw drop.
So if you have an allegiance either way, or a particular affection for a console-exclusive series, feel free to follow your heart. Maybe you're holding out for a new Uncharted, or maybe you need need neeed Halo 5. Fortunately, both the PS4 and the Xbox One are hearty, capable consoles that can play games, stream video, and connect you with your friends just fine. But, in the absence of games you actually want to play right now, the Xbox One can do more things straight out of the box with its various media and interface tricks, no games required.
You should: Follow your heart, but go Xbox One if your heart can't decide.
If you have the slightest amount of self-control
What almost everyone should do is wait. Wait wait wait wait wait. Don't buy anything just yet. Launch hardware has a history of being a little wonky. The Xbox 360 had that huge red-ringing problem, there are at least some PS4s out there suffering a blue light of death.
And even if your console hardware works perfectly, there's just not too much to do with it yet. Sure, there are pretty launch games out, but those aren't the real must-plays. Watchdogs, Titanfall, Halo 5, Uncharted: Whatever, Destinylthese are all months away, at least. Why not hold off until then, if not longer?
So relax. You should buy a gadget for what it is, not what it's going to be, and unless there's a launch title you're for some reason positively desperate to get your grubby little paws on, both these consoles are just over-priced set-top boxes for now. Who knows how things will shake out in the coming months and years. Besides, if you can hold on long enough you'll probably be able to pick up either for way less cash.
You can do it. Deep breaths. There we go.
Almost everyone should buy: Nothing yet!