Let's put the fan-centric arguments of who "won" aside for a moment.
Microsoft gained some ground in the installed base segment, which is always meaningful early in a generation. More importantly, they chipped away at the PS4's previously unassailable image of invulnerability, giving them a nice PR platform going into Christmas. On the downside, it cost them a hell of a lot of money. Now, someone is going to say that Microsoft doesn't care about money but that's bullshit. They certainly care, they're just not afraid of risky investments.
Sony, who "lost" the month, sold around 800k units at nearly full price. Think about that for a minute. They could have gone head-to-head with Microsoft with price cuts but I think it's obvious that they'd rather take the profit. Of course, the things they gave up are meaningful. It's not a strategy without costs. Momentum in North America belongs to Microsoft right now.
All of that is why who "won" is such a simplistic question. I think both companies come out of this satisfied but not ecstatic. Each went for what was most important for them, and did well, but they both paid a price.
Anyway, as I've said before, this is a cycle that repeated all throughout the PS3/360 era and one that is likely to be repeated throughout this era--Sony pulls away in the first three quarters of the calendar year, Microsoft makes up ground in the last quarter.