I have some UA stuff, I think it is the best base layer you can buy to keep warm. However I can buy athletic base layers made of 'moisture wicking' material from walmart for about 5-7$ each. SO I have a ton of that stuff, but on the coldest days I usually wear UA.
My only complaint with UA is it seem to be more uncomfortable than my other base layers, it rubs against any body hair and kind of makes me have ants in the pants. IDK, maybe I'm just crazy.