In all honesty I wouldn't buy either console yet.
We are still in a period of transition, where it's too early for there to be any games that are exclusive to either next gen console. Certainly none that are worth shelling out £400 for anyway.
Instead what we have are both current AND next gen versions being released for all games currently on the market, or due to be released over the next few months. Even Microsoft's main attraction Titanfall is also being released for the 360 (and PC), while I feel is a big mistake. Make that game exclusive to the One and you might have a system seller. Doing it this way, they don't.
There's a new Metal Gear Solid game coming soon, but again it's also releasing for the PS3/360 - so just save yourself some money and buy the current gen version.
I bought a PS4 on launch day, and I was bored of it after a week. Haven't switched the thing on since then, and that was way back in November!
As I said, there is currently no reason to own one.