I'll say PS4. As of now it has a better slate of games releasing in 2015 and I expect Sony to have much better deals during the holiday season to compete with the XBO.

To the bolded part: Isn't the first 9 ish months of 2015 going to be just as baren? Worse even, since it won't have a big game to bundle the crap out of? Also, what are the odds that Microsoft will have the value advantage that they had for the 2014 holidays? 

The reason I think the PS4 will carry the U.S. is that I see MS having a weaker first half of 2015 and Sony being more competitive in the second half.

All possibles, I agree. But I think it's just as likely ms will want to do something not to revert completely back to PS4 destroying them. (Price parity and the negative baggage will help). We don't know what MS have E3 onwards. They have a lot of games coming, more than last year anyhow, don't think they're all gonna be bunched up together again. Who will debut a slim this year? If either? Strong rumours for XB1 slim and I'm sure penty of PS4 ones will pop up again. Are Sony in a position to cut to $299? Regardless of cutting costs.

The Order is february, Bloodbourne is March. What else do they have (before I get into a discussion about their line up and the implication on sales) I want to be fully informed.

1. 3DS
2. PS4
3. XB1

I don't know if the 3DS will ever reach 20m in the US. Maybe 18-19m?

I honestly think the New 3DS will help get it to being first to 20mil, it may not "revive" it like you said but it will definitely help get it there first.

We still have to see the long term effect of MS deals. And for now, i am not convinced.

So i am trusting PS4 victory by default first, 3DS miracle second and MS $100+ deal not being a "Fire sale" last. And don't get me wrong, i agree that XO will most likely hit it 20M before 3DS, but imo doing that before PS4 is harder than N3DS being bought again by 3M.

Despite HALO, which is indeed huge, PS4 will keep outselling XO during third party releases. MS can only turn this around if they keep burning money (what i am sure they CAN do, just don't think it is what they WANT to do). In the end, being second to the PS4 is not actually bad and they can profit from it.

this is why sunset overdrive, which got great reviews, is outselling littlebigplanet 3 big time, which got mediocre ones.

wait, wha? only 100k? losing by a lot ww? well i'm sure forza horizon 2, with its great reviews, is beating driveclub, with its near unplayability? oh no? they're tied, you say? but then there's the multiplats, xbox one advance warfare is surely outselling ps4... you mean it's not (winning in us barely, losing big time worldwide)? but wait! what about assassin's creed unity, that was bundled with every xbox one sold this holiday, practically, at $50 less than the ps4... oh, well, at least that's winning. in the us.

I would have said Microsoft but since their brains broke and they decided to raise the price back I guess PS4 will have the advantage. PS2 got it's first price drop of $100 roughly 21 months after launch. If PS4 follows that pattern they'll have a price drop this June. Which coincidentally, is right around E3. Though I think it'll be $50 instead of $100.

Talking about the lineup, PS4 has the clear advantage 8 or so months before the holidays. The Order, Bloodborne, Ratchet and Clank, Until Dawn, MLB, Tearaway, and maybe a few Japanese titles depending on when they get localized. XBO has Fable and Screamride?

The holidays will be Halo vs Uncharted. Halo will win but Uncharted is no slouch and I think they'll be pretty close sales-wise. Both will push a lot of consoles. Tomb Raider is on 360 and a lot of people still expect it to be a timed exclusive so I don't think it will be a huge system seller.

If they're both $349 by the end of the year then PS4 will easily win. XBO can't outsell it at price parity. XBO might be $299 by then though so we'll see.

And is 3DS even going to reach 20m in the US?

I think it will be the 3DS: largest market size, lowest price point, and biggest lead.