I've used both AC Vws and Corvairs in serious winter conditions. The VW would go anywhere with snow tires mounted, but the heater (it was a '63 in very good dondition) was nearly useless - commonly drove with a blanket on the lap and an ice scraper at hand for the inside of the window.
The 'Vair, though , was great! It was a '63 (this was in '68 - 70, so the car was in very good condition) and the standard heater would roast you out of the car. I could commonly drive with a light jacket when the outside temps were below zero. The only thing about 'Vairs is, you have to be sure that the pushrod tube o-rings have been replaced with Viton, and that the exhaust manifold packings (gaskets) are in excellent condition, or you can get exhaust fumes or hot oil fumes in the heater boxes that blow straight into the passenger compartment. These parts are commonly available from places like Clarks or Oregon Corvair Underground, and you can replace all of the above easily in a weekend. The exhaust manifold/heater design is really the only true design flaw I can note with Corvairs, particularly late models.
Both my father and I drove through snow over the headlights on more than one occasion with our various Corvairs. Without snow tires or chains.