Merino in light-mid weight if I'm hunting afoot. Heavy or Expedition weight fleece if I'm going to be stationary. In the coldest weather I wear "High Pile Fleece" from "Clam", the same company that makes portable ice-fishing shelters. They call this their "Sub-Zero" base layer. I call it my Gray Wookie Suit.

Wookie Suit

I can walk on water.......................but I do stagger a bit on alcohol.