It was announced that there will be many surprises from Nintendo during E3 2010. They'll reveal the 3DS, Zelda Wii, Metroid: Other M and other things. But I'm pretty sure that Nintendo will announce an even bigger surprise, a new version of the Wii or a completely new console to start off the new generation of video games with awesomeness.

3DS is gonna be huge! 3D pokemons and nintendogs... how can you beat that?

answer: you can't

probably 3ds, becAause it's the sussesor of the almost most sussefull sistem of all time

The Wii2 will be realeased in 2012, not before. But anyway, there's a great problem for home consoles: Japan. We're seeing that even the most succesful consoles combined (PS3 and Wii) aren't selling like the best portable many weeks, and PSP, which is quite dead in the rest of world, is constantly outselling every home console!
Considering this and the fact that every Nintendo handheld was succesful I would say that the popularity of 3DS is quite sure, while it's not sure (and, I would say, unlikely) that it'll sell better than DS, the best selling console of all time before the end of the year.
Wii2 can be a very good purchase if Nintendo adds all the functionalities the Wii lacks this gen (online, HDD, many SKUs, achievements, HD), manteining all the great content it has (we cannot deny it: the Wii has a lot of great games, mainly first party but not all). I think the next Nintendo console will be succesful but not as much as the Wii, which IMO will be able to sell over 110m, becoming the 3rd most selling console of all time.

The 3DS, by a mile.

I think 3DS.

The future is heading towards portability. The next portable consoles might have graphics and online capabilities on par with Xbox1.