I'm sure that it'll be the 3DS, but you never know.

3DS will take it in my opinion. They just have some very big heavy hitters in terms of exclusive titles/franchises.

Vita will do well, but I think they will need to do some price cuts to get close to 3DS sales. Also 3DS already has a lead.

Anything can change, but I think the cards are stacked against Vita right now.

nintendo fans will say 3DS will win...
and sony fans will say VITA will win...

even chances.

like with most timed exclusives(MH included) psp fans have to know or at the lest think MH4 is coming to PSV.

In terms of overall sales it will be 3DS, but I say a few months after Vita launched, weekly sales could be on par.

not all the time

The main problem I see with the vita is the price. You need to pay 25000 yen for the console, then pay at least 2200 for a memory card, and then pay 5000 for a game. I think the price makes it only atractive to core gamers. I can't see a parent paying so much for a handheld for their kids. So I have to go with the cheaper 3ds with 2d Marios, Mario Kart, Animal Crossing, pokemon and now monster hunter. MH doesn't have to be exclusive to the 3ds. just having it alongside pokemon is a win for nintendo.

3DS will sell at least three times as much as Vita. In Japan, it's not a competition anymore. The only reason the PSP isn't dead there right now is MH. With MH on 3DS, and likely exclusive, Vita has nothing of much worth on its side compared to 3DS.

It's hard to say....
In Japan with 2 Monster Hunters going to the 3DS the Vita got a big kick in the balls and if Nintendo is able to pull exclusivity somehow then upgrade the kick to shotgun into the groin. Currently Japan is leaning much more towards 3DS since sales in Japan come greatly from big name games which Nintendo has seemed to secure as well as their first party games which are part of those big name games class. Now Others and Americas are hard as hell to tell whats going to happen. In both sales come from overall library, with Nintendo shooting themselves in the foot with the after launch drought fiasco and how unpredictable the vita games will be received it's hard to tell. The first signs of whats to happen in either will be with the sales of Mario 3D, Mario Kart 3D and their affect on the hardware sales though these will be badly skewed since both are coming out during winter so we won't see the effects until early Feb. On Vita's side it needs to be able to sell software and franchises in the west unlike it's dad had trouble doing so. Right now as others have said 3DS does have advantage with it's current strong Japanese Lineup and being the son of the DS but, like in everything in life things can change quick by either self-implicated problems or outside forces.

Too early to tell, but it'll be a lot more levelled this gen that's for sure.