First of all, the Vita isn't dying, it's launching....there's a difference. It's a late bloomer just like the PS3.
That being said, I say the Wii will win. Not only is it cheaper and more family friendly...wait...that's pretty much the only reason really...
The Wii U launch won't have much of an affect on Wii sales unless Nintendo decides to kill it early like they did the DS.