I always run snow tires.
My old Ford Taurus with good snow tires was 100% my choice of vehicle to drive anytime the weather got bad.
Why? The snow tires gave it the traction it needed to dig through anything. The more agressive tread on the snow tires also helped when I would hit slush or even be driving through snow on the highway. Also, being a front wheel drive car, it was VERY heavy in the front and EXTREMELY predictable in the snow. Jeeps and a lot of other typical 4x4 SUVs tend to not be predictable or stable in the snow.
I've had my Focus through one minor snow storm when I first got it. While it didn't do terrible, it didn't do as well as I had hoped. I really don't feel comfortable driving on all seasons in the winter.