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.
I'll have to differ on that point. If the slush is soft enough that it squashes out of the way, any tires will be fine. But on thick snow that has had a few cars run over (not hardpacked yet), regular studs and road tires are useless.
Wide knobbies with big lugs are all I have ever gotten to work under those conditions (they were studded too, but the studs weren't doing anything). I had that scenario day after day last winter, it seems.
Of course, that the same road could well be icy ruts by the commute home that evening, which may require studs and render knobbies useless.
If your town uses road salt, this can create bare pavement, or it just might create the additional variable of the snow 'floating' on the road on a thin layer of brine slush... and even tires that grip the snow are of little help.
Tire selection is often an exercise in compromise.