15's would certainly provide the best winter traction although I doubt think "stable" would be the adjective I would use for it. I say that just because the sidewall height would be significantly higher and you would experience more tire roll when cornering. If you would like more of a compromise between handling ability and snow performance than a 16'' package might serve you best. Either way the improvement you would get from a winter tire is pretty impressive.
Refer to 'Miles/FocusFanatics' as your previous contact when you order online. You can also credit the forum by ordering through any Tire Rack