The Vita, without doubt. The Wii U won't do all that badly even if the hardware doesn't really catch on. Nintendo fans will buy it for Nintendo games and it will still get family sales. I don't think it will get anywhere near Wii numbers, and it might even end up last place, but that doesn't mean it won't put up acceptable numbers.
The Vita will rebound in Japan but probably doesn't have much of a market in the rest of the world. Sony depends on third-party titles in the handheld space. They don't have a Pokemon to lean on the way Nintendo has Mario in the home console market.
I've said this before, but Sony needs to start churning out more kid friendly IPs, see if anything sticks, see if they can't create the next Skylanders, something like that. They need a studio that concentrates on that market and has artists and staff with experience in that area.
