Hard to say, but I'll make a guess.

Wii U: 18-25 million

3DS: 80-90 million

I'll take the average and say somewhere around 21.5 million Wii U's and 85 million 3DS.

The Wii U was poorly designed and hasted out the gate to counter the incredible and sudden decline of the Wii, it lacks basic appeal, at least that's my theory. Seeing the tiny effects of software and price cut, and the short time window of effect on both accounts, this is looking more and more likely, Q1 and Q2 2014 will be conclusive though, even if it manages a decent holiday, that doesn't mean much, it had a very good holiday season last year and we saw what difference that made for the remainder of the year. Squeezed between the 7th and the 8th gen, it will probably be slaughtered on all points, from profitability, software sales, support and hardware sales from one competitor or another and it will likely be replaced a lot sooner than the Wii was.

The 3DS will fall victim to a collapse in the dedicated handheld market due to tablets/phones devouring marketshare and stealing the entire casual base (this has all but happened already) and the more core gamer will get their fill with home consoles, mirroring on smart devices and more core games arriving for the tablets and phones as the market expands and attracts more serious customers. We're already seeing this development in Europe and Japan, digital distribution will also contribute to this in the long run.
The DS had three consecutive years of over or around 30 million (!!!) consoles sold, the 3DS will never get anywhere near this and has a probable peak around PS3/360 levels right now and is set to track about 12 million below the DS after three years on the market now in february despite initially tracking above, launches aligned, this is is very similar to Wii behavior, only a lot sooner and in spite of reduced price and good support.

How is 3DS peaking around PS3 and 360 levels? So which do you think will have higher lifetime sells PS3 or 3DS?

Hard to say, but I'll make a guess.

Wii U: 18-25 million

3DS: 80-90 million

I'll take the average and say somewhere around 21.5 million Wii U's and 85 million 3DS.

The Wii U was poorly designed and hasted out the gate to counter the incredible and sudden decline of the Wii, it lacks basic appeal, at least that's my theory. Seeing the tiny effects of software and price cut, and the short time window of effect on both accounts, this is looking more and more likely, Q1 and Q2 2014 will be conclusive though, even if it manages a decent holiday, that doesn't mean much, it had a very good holiday season last year and we saw what difference that made for the remainder of the year. Squeezed between the 7th and the 8th gen, it will probably be slaughtered on all points, from profitability, software sales, support and hardware sales from one competitor or another and it will likely be replaced a lot sooner than the Wii was.

The 3DS will fall victim to a collapse in the dedicated handheld market due to tablets/phones devouring marketshare and stealing the entire casual base (this has all but happened already) and the more core gamer will get their fill with home consoles, mirroring on smart devices and more core games arriving for the tablets and phones as the market expands and attracts more serious customers. We're already seeing this development in Europe and Japan, digital distribution will also contribute to this in the long run.
The DS had three consecutive years of over or around 30 million (!!!) consoles sold, the 3DS will never get anywhere near this and has a probable peak around PS3/360 levels right now and is set to track about 12 million below the DS after three years on the market now in february despite initially tracking above, launches aligned, this is is very similar to Wii behavior, only a lot sooner and in spite of reduced price and good support.