Hasn't Wii U already outsold the PS-Vita global sales?
That said "portables" generally outsell home consoles... this is because gaming households can own more than 1 of the same portable but rarely ever own more than one of the home console.
So if the PS-Vita has anything like PSP success down the road then I think it will outsell the Wii U lifetime. I don't expect Wii U lifetime sales to be as good as Wii, PS3, or X360.