Fat or Skinny Tires for Winter Riding? Fat or Skinny?
I think the arguments are as follows:

Fat: You can float on top of the snow and you don-t have to go through it.  You have a larger contact patch with the ground.
Skinny: Will find it's way through the snow to find some pavement to grab onto.
Studded: Works great on ice but has no effect on snow/slush/other stuff.  (Note never tried studded tires so just speculating).

Conditions of Interest
I am interested in traction on:

Cleared city streets
Uncleared city streets



Uncleared city streets where cars have gone through and made deep ruts



Slush



Slush that has re-frozen into deep ruts
Ice patches

Note: All pictures are take from google images.
Background
I have a short commute through part of Ottawa and run lots of erands on my bike.  When it is snowing and when the roads don't look good I have several routes that are only slow residential streets so I can stay away from people yacking on their phones.
I would also like to start doing some winter trail riding.
Here is the historical weather data for Ottawa.
I live in a country which doesn't have snow, but have recently gone to Europe (Czech Republic), where I could "understand" a bit how these things work. Also, my background is with mountainbike on any sort of offroad terrain, including mud and beach sand.

That being said, I think your most concern would be the grooves/ruts from refrozen snow on roads, much similar to sun-baked mud on some fire-road tracks, but much more slippery, and flotation, much similar to riding on loose gravel or sand (I am speculating a bit).

I can see a lot of studded tires are also slightly pending to the knobby-fatty end of spectrum. With wider tires (no need to be super-wide), you can use lower tire pressures to float better and yet don't get pinch flats. Also, with wide AND knobby tires, you can much more safely ride diagonally through ruts without the danger of your front wheel getting caught and you fall.

So, that's my (also a bit speculative) impressions about effects of tire width, tread-pattern and inflation pressure.

Hope it helps!