For me, it might be the Wii U.
Have you tried one before? For oldschool games it might be decent, but my boss has one and hates it (I think mostly because the touch screen is resistive and not capacitive (i.e. not very good)), saying it seemed like a regular Wii with a poor touch screen added.
I voted Ouya and Xbox One. My work already bought me an Ouya, and at work we have a couple. They are *awesome* when it comes to playing old school games on an emulator (kinda sucks you can't get ROMs legally), but then again I might have been just as happy with the Wii U (
but then again, Wii U can't do SEGA gamesedit: perhaps I was mistaken).
I might get an Xbox One. And by I, I mean my parents/family. I hate the idea that some games might require an always on connection (but then again, I hardly game anymore). I'm not sure how the all-in-one experience is, but it might be nice for my parents. I guess we'll see.