I'd go for the PC simply because you actually get third party support with it. The big problem with the Wii U is Nintendo is pretty much the only developer making software for it. As such, the pace of releases are very slow, and if you want to play anything aside from what Nintendo puts out aside from a few indies that get ported to Wii U, you're largely screwed.
Unless you're such a huge fan of Nintendo's franchises that you are willing to pretty much sacrifice playing anyone else's games in order to play Nintendo's stuff, I'd say go for a newer PC.
Unless you're such a huge fan of Nintendo's franchises that you are willing to pretty much sacrifice playing anyone else's games in order to play Nintendo's stuff, I'd say go for a newer PC.