Obviously we don't know what WiiU will do this holiday but if there's a Vita pricecut I could definitely see this happening.  Vita has had a monster couple weeks with a pricecut in just one region.  We'll see what's coming later this year other than Tearaway and Killzone at E3, but I think Vita could actually pull it off.  WiiU probably won't cut price this year, but if they have a Mario Kart or 3d Mario for the holidays that looks good then the situation changes entirely.  I'm saying Vita for now.

EDIT:  Holy crap this got a whole lot more popular than I expected.   129 for WiiU, 110 for Vita, and 17 for Dreamcast.  Looks like a pretty even running though Virtual Boy is losing with just 4 as usual.

ill say the WiiU

Hard to say, because both consoles are still struggling.
While Vita had two great weeks on Japan with the price cut, but its sales barely surpassed 3ds on its worst week after its price cut last year. Sony must keep a good flow of great games releases and bring the price cut to other regions.
The WiiU seems to have a more promising lineup for the rest of the year, but without a price cut it´s hard to believe that it will sell as good as the cheaper competitors.

Of course this is just a very, very simple view of the situation, but i´d bet that they will be even, with the WiiU selling a little better than the Vita.

Wii U, will sell ever so slightly more than the Vita (let's say 500k more) because of Mario Kart, 3D Mario, and Wind Waker.

Also I see a price cut coming which would boost the gap even further.

I say wii u. You have to remember that even though the vita got a price cut, it also got many new, important titles at the same time. And the wii u will probably get a few important ones later this year.

you think it's getting both MK and 3d this year?  I don't think an HD remake can push sales I mean I've never seen one do that

Ah, interesting thread, thanks. Would you be so nice to bump this thread at the end of the year? It would be great to see how the expectations turned out. I personally voted about even. I see both Sony and Nintendo working towards better sales, that will probably have similar effects.

I'd say Vita.

The Wii U is simply not interesting enough as a console. But who knows, we'll see.

But you've never seen a Zelda HD remake, have you? ;) Ocarina 3D did a decent job selling 3DSs, but would've done better if it had had company. As for Mario, both will be playable at E3, so I think it's safe to suppose at least one will be released this year.

Learn something son, anytime you put Virtual Boy in a pool, no matter what you ask, I will always vote for Virtual Boy.

Also, WiiU will sell more when the Nintendo exclusives arrive.