All of these consoles are amazing, but right now, I would say that the Wii U and PS4 are the best consoles. I honestly see no reason to buy an Xbox One right now because, while it is amazing, it is essentially a more expensive PS4 with a few changes added in.
In the future, however, I expect the PS4 being the best console, the Xbox one being the second best, and the Wii U falling out of existence if things continue going the way they are. Right now, Nintendo has a very limited number of 3rd party companies backing them up and the ones that are are supporting Sony and Microsoft more. That being said, I have faith in Nintendo to make excellent 1st party games that will increase sales and attract 3rd party companies to make games for them.