There is just too many factors for the Vita to succeed. So I would go with the Wii U since it only needs Ninty IPs to sell.

Well vita got a boost from Vita TV in Japan and then that dropped like a rock, so in japan, we should see Wii U outselling Vita routinely. In the US, if Black Friday week is any indication, consumers arent really down to buy a Vita. In Europe, even with Wii U doing pretty damn terribly, it is still keeping up with the vita for the most part.

Additionally, Wii U has more system selling software in the pipeline.

Unless Vita catches on as a PS4 accessory or Vita TV is a HUGE hit in the West, I think Wii U should make it to 10 mil first.

From an objective pov : Vita because more games coming, good support from first party+third party unlike Wii U with just first party support.

also, Vita sold more per week than Wii U this year  and will reach +7M in 3 weeks

By years end I bet the PSV will have passed the 7 million mark and the WiiU will have passed the 5 million mark.
Both can received a big sale boost after the holiday season if Sony or Nintendo drop the price.

2014 could easily be the year of the WiiU, if Nintendo drop the price to $250 and there no major delays to the big release. The WiiU line up and potential price cut should make 2014 a much better year then 2013. By the end of Summer Nintendo could potentially be around the 10 million mark.

Feb and March seem to be good month for PSV and the release of a new edition of PSV tv ..... could be the boosted needed. Since i'm assuming that PSV will have sold 7 to 7.5 million consoles by year end. They only need to sell less then 3 million to reach 10 million ... I presume that the sales will be better then last year, PSV could easily sell 2 million between January and March 2014. There for by mid-summer they would reach 10 million.

My bet is that Play Station Vita will reach 10 million first by a few months.

vita though the wii u will have sold more software by then

Updated with list: And damn some of your guys user names xP

vita considering sony is release the vita bundles in NA soon.

WiiU will sell a lot through christmas, has system sellers coming, and vita is overshadowed by the 3DS, so the WiiU

Vita, because it has recently found its footing in Europe and Japan and it was still outselling the WiiU on a weekly basis before that. Factor in the 2mil+ lead and it's a logical choice.

I'd say the WiiU has a higher chance of making a quick turnaround though, Mario Kart 8 could definitely make a dent.

Vita, because it beats the WiiU sales most weeks.