how do you define "best"? light weight, warmth, shelter from elements,?? What works during a relatively calm winter night could be life threatening during a raging storm. I have spent lots of winter nights (around 0 F quite comfy in a bivvy sack, perhaps with a light tarp pitched as a leanto. The bivvy sack adds 5-10 degrees of warmth to the rig. A three season tent will work well until (when) you encounter a storm. With snow and wind, you want one rated for four seasons, with good reviews. My worst bivvy was on the San Francisco Peaks in late December. Tried for a snow cave, but the snow was total powder and I had a snow hole instead. Temps were around minus 35 F. No sleeping bag, just an extra sweater. I did have a small stove, otherwise I might not be here today. It wasn't the best, but it was good enough. Selecting a sheltered location can make a big difference. Avoid the bottom of creeks and drainages and obviously windy places. Asmall cave or rock shelter can be quite good.
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