I actually own both and enjoy both so please don't think this is me bashing one or the other.  I do however want to hear people's predictions on this though :)

Things to Note (Or in my opinion)

-WiiU has a brighter future in current Software Lineup

-Vita had a headstart

-Both Sell similar to eachother on a weekly basis

-Vita is being treated as a high end accessory to the PS4

-WiiU is supported by extremely popular Nintendo Ip's and Mascots.

Predictions for Vita to Reach 10m First

Tbone51
JoeTheBro
aryu
Blowoverking
BHR-3
curl-6
aerys
yvanjean
WonkTonodi


Predictions for WiiU to Reach 10m First

AnimeGaming
Jizz_Beard_The_Pirat
Busted
TheGhosts
busbfran
Damian.W
Kaiwaix33
007BondAgent
tripenfall
locknuts
STRYKIE
EricFabien
Archbrix
tiffac
sundin13

if smash and mario kart comes out early next year both those games will make the Wii U reach 10 million before the vita does

Vita. Up until a week or two ago it was outselling Wii U every month since January I think.

Hard to say as their are many reasons for either reaching ten million first.

The PS Vita has currently sold more consoles

The WiiU has sold more per week on average than the PS Vita

The PS Vita has cross play with the new and very popular PS4 and may therefore spur on more console sales.

The WiiU has arguably better first party support for the console.

While I'm sure I've missed many reasons either way I am going with an indecisive 50/50.

Either way their both great consoles with great games.

The answer is clearly "neither." Duh

Going to have to go with Vita at this point.

The Vita "should" get to 10 million first but theres 2 wild cards that may determine which gets there first.

1. being how Wii U performs throughout the holidays. Nintendo consoles are known to go into beast mode during the holidays (just look at 3DS) so if it has a strong holiday it could cut the gap down by alot.

2. If/When the Vita's new model and VitaTV get's released in the west. I doubt either will be at 10 by March so if the Vita 2000 and VitaTV is released in US/EU by then, then the Vita should get there first.

oops i mean, why are we comparing handhelds to consoles? there completely different because blah blah blah herp derp.

WiiU cause of all the games coming out in 2014 but hard to tell at this point

hahaha, silly man, the vita is never going to reach 10 mill... lol