This thing, if you want warm. It's called the Seirus Ultra Clava. You can just use it as a mask, just use it as a balaclava-hood thing, just use it as a gaiter, or use it normally.
It's up to you, it's super warm and doesn't fog. I don't know, as I look pretty silly here:
Overall, warm and nice. Can wear it multiple ways. $25.
Yowies and buffs are both a joke. Get a plunkshun mask, they're using far superior technology that no one Is using (I.e. they will never get wet and freeze, clump, etc)
Armada Ballerklava. If you're going the balaclava route, you need to get a two piece, and the Ballerklava is the cheapest two piece balaclava I've ever heard of. At 20 bucks, it's not a horrible idea.
and my personal favorite, especially for when its cold, an ec ninja mask:
i would definitely reccomend any of these, but if you had to pick one get some sort of balaclava because they cover everything and can be pulled down when needed. hope this helps