There are those who disagree, but I'm of the opinion that if you're going to be riding below freezing, studded tires are a must. Knobbies are for mud. On ice they're no good. You need studs for that. Unless, of course, you *like* falling in front of traffic...

Road tires are just fine in snow and slush. Knobbies offer no great benefit there either, although there might be some benefit on hardpack.

Now if you're going off-road, that's an area where I have no experience, so I couldn't say.

But you said commuting, so I'm assuming pavement. Skip the knobbies. Stick with the road tires if it's not icy, or get studded tires if it is.