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.
one or more gifts or other benefits from the co-op.