I'm out of the console game now (I'll hop back in when my kids are old enough to play with me), but if I was buying a new system, it'd be the PS4. This is a HUGE departure for me because I've been hardcore Nintendo my whole life. I owned PS2 for a short time between the GameCube and Wii coming out just to bridge the gap and play KH and some Final Fantasy titles. Other than that, it's all Nintendo all the time.
The Wii U just looks like the Wii with a humongous controller. The 2nd screen is a very cool idea, but a lot harder for 3rd party integration, especially if the title is cross platform. The information on the 2nd screen could help clean up the HUD on the TV or make it quicker to access menus and so forth. But so what? It looks like the Nintendo exclusive titles could be fun and innovative with it, but once again Nintendo alienates a lot of cross platform developers.
I find the Xbox's holistic approach intriguing, but it has not doen anything to sell me on it's capablities as a gaming machine. I'm sure you could do some epic Sweatin' to the Oldies workouts with it's schmancy new camera, but I typically play video games when I'm in a more sedentary and vegetative state. I balked a little at the Wii's motion requirements, so full body stuff doesn't appeal to me for the type of gaming I like on a regular basis.
Also, the Xbox One is a blatant grab at a peice of the home ecosystem that is currently being set up by other companies, most notably Apple. It makes sense to have lots of devices that work together and create synergy, but until one company becomes the clear leader or they learn to play nice and let their devices interact, I'm invest the money into a system that may or may not exist in 5 years. I would want to see how the Xbox functions as a hub and if it's really worth it to revovle my entire entertainment ecosystem around it. Personally, I'm not willing to bet on Microsoft right now.
So that leaves Sony. I think they are delivering what gamers want- awesome games with fantastic graphics and access to features like sharing, virtual consoles, and dlc. They seem to be keeping it simple. Doing everything they do well and doing it better and faster.
As a peice of hardware, I think the Xbox One will appeal to more non-gamers and therefore could outsell PS4. But for the gaming faithful, the PS4 seems like the way to go.