The Wii U
As an owner of both a Wii U and a Vita, and loving the hell out of both, Nintendo is just honestly handling the Wii U much better than Sony with the Vita.
Both consoles essentially went through a very bad patch and so far only Nintendo chose to stick with their product and things are working out pretty darn great for them now, there's already a handful of fantastic exclusives out for it and tons more coming. The Vita on the other hand, has...errr... Gravity Rush 2 maybe? Yeah, Sony threw in the towel with it sadly (so far, still clinging on to false hope here) and is leaving it in the hands of Japanese and indie developers now, the latter making some fantastic niche games but lots of them sadly never having much of a chance getting localized from what I've heard and unless playing indie games on a portable is a major dream of yours, you can grab those on another platform you most probably have anyway.
Heck I'm surprisingly enjoying my Wii U tons more than my PS4 which I've had for over a year now and the Wii U only a few weeks, between Hyrule Warriors addictive gameplay, Bayonetta 2 offering one of the best action experiences ever, Wind Waker HD charming my pants off and my backlog of other good ones like W101, Mario World and MonHun waiting to be enjoyed immensely, I'm genuinely feeling that long-lost magic I had with games when I was a kid and I'm loving it. The console itself is also fantastic, the store is charming as all hell, the interface is a delight to use, off-tv play is awesome and I love the fact that it allows me to use my gamepad as a remote for my TV. Its also great having it docked in front of the computer too because I can just easily access the internet through it and search up a guide when I get stuck in a game or something. Also recently set up a media server which is Wii U compatible so I can enjoy some off-TV screen movies now too when I feel like taking a break.
Go for the Wii U, the Vita is great but honestly something only worth grabbing when you find it on a very good special. You can make use of the Wii U's backwards compatibility for now to get your RPG fill with Xenoblade Chronicles, The Last Story and Pandora's Tower and such until the new Xenoblade or whatever else comes along.