Originally Posted by nathank

AWD: again, never actually seen a setup, but i think (also like 4WD cars) that AWB would only help in propulsion and not be much of a safety factor.
but yes, i see no reason why studded tires and AWD would not be good --- unless you need special wheels and so it's a pain to change-out wheelsets and/or tires.

Tri: i have never ridden a tricycle (as an adult) but yes, obvious stability here. not sure of the drive issues (you commented on that) but in deep snow with weight on 2 wheels the forward motion is probably worse than weight on one wheel.

mountain bike has following advantages:
1) wide choice of wide tires and studed tires and basic setup has wide rims so wide tires actually mount "wide" (i find around 2" is the best compromise for snow/ice as for snow you want a relatively wide tire that "floats" and for ice you want a narrower tire that "cuts through")
2) good/durable in snow/slush/dirty grundge
3) wide straight bars and nimble upright riding position so maximum bike handling capabilities (i.e. putting a foot down going over ice is easier on a MTB than road/cross/trekking) -- i.e. one of the top design considerations of most mountain bikes is handling and stability at all speeds (low speed on a MTB better than road/cross/trekker - just try doing a track stand and you'll see the difference!)
4) good brakes (either V-brakes or disc)
5) generally space for fenders (not mounted super-close to the tires b/c of snow build-up)
6) low gears for cranking through snow

i personally find the 1.9/2" wide MTB "semi-studs" to be the best choice for commuting as they perform reasonably well on the road at regular pressures (say 35-35 psi) so a good compromise between speed on hard surfaces and safety for ice. then for major snow/ice you let the pressure down to 15-25psi and get a bigger contact patch and more stud contact.

i put my semi-studs on for the first snow - around end of October here - and then leave on until mid-May or so.

i also own an agressive studded tire (2" wide 26" MTB tire with Major knobs and like 300 studs/tire) which is awesome on ice and snow, but it is SLOW and annoying on paved surfaces. i personally do not see a need to use mine for commuting but i do agressive winter mountain biking (e.g. i mountain bike down an ice/snow sledding/luge course where having this tire in front provides awesome traction/safety)

for commuting where safety is much more important than efficiency (and money not much of an issue), you could buy a 2nd wheel and put the agressive studded tire on that and on major ice-risk days with good ground snow coverage (so little or no paved surfaces) just change out the front wheel, but here you have the cost for an additional front hub/rim as well as an agressive studded tire which costs like $50-70!

P.S. for winter i personally recommend riding with flat pedals (or better yet BMX-style pedals with pins) and wearing warm winter hiking boots.
i have tried various winter bike shoes with clipless pedals and overshoes and whatnot and the WARMEST method is hiking shoes. the main problem is the metal cleat on the sole transports col direclty to the inside of the shoe! in winter the slightly lower efficiency from not having clipless is worth the warmth, extra security if you need to put a foot down as well as nice if the snow is too deep and you have to walk a bit.