I've always used UA as well. I see many people calling it overpriced, but it's what I have used and it works very well for me.


I have the original skin tight UA that I wear most days in the winter. If it's really cold or I am outside for a long time I wear 3.0 or 4.0. Stand hunting in late season? Combine them.

 
That underwear is some of the best money I have ever spent.

Been using merino wool almost exclusively since moving to MT and working outside all day.  If I sweat,  I don't get cold.  And it doesn't stink up so I can use two sets for a weeks worth of work.

This

 

Good cold weather gear isn't cheap.  And 2nded on the happy ball underwear.  First time out with them and I bought 5 pairs later, they could charge 40 bucks and I'm still buying it.

I have an outdoor aquaponics system.  I don't shut it down until the nighttime temperatures hit 27 or 28.  "Cold as fuck" is relative I guess.  

On a serious note, there are many materials that make good base layers:

1) Merino wool
2) Polypropylene
3) Polyester
4) Silk
etc.

They are all comparable in that they all wick sweat/moisture away from the skin which helps slow down conductive heat loss.  They come in varying "weights", such as Patagonia's Capilene Polyester which has 4 different thicknesses and designs.  The differences between the different materials are:

1) Some wear better
2) Some wick better
3) Some dry faster
4) Some are more UV and heat resistant
etc.

I don't think the differences are enough to make one material that much better than another unless you are using them for a specific application.  For generic hunting and fishing, you will be well-served by any of them.  It boils down to price and brand.  You also do want different weights for different temperature ranges.  

I have used polypropylene, Smartwool and silk.  This was the first year I've tried Patagonia Capilene, both 3 and 4 weight.  

ETA:  A quick note about cleaning:  Sweat has 2/3 the amount of salt as blood.  As salt and skin oils collect in the fabric, the wicking ability of the fabric suffers.  If you let it air dry you can get several days of use out of it, but it does have to be cleaned to restore it's full wicking ability.