I have had the "privilege" of being able to train in everything from subfreezing temperatures to triple digits. After trying just about everything under the sun (or lack thereof in some parts), I found that if you still want reasonable dexterity when it comes to handling a rifle or gear, your fingers are never going to be fully warm. So what I have done is purchase a pair of thin glove liners (I have used both Serius and Polartec with good results) and wear them under whatever tac gloves I'm wearing at the time (I prefer Mechanix Wear, also liked the Army issue nomex flight gloves). That provided a reasonable amount of protection while moving around and doing stuff without too much of a loss in dexterity. I could also take off the outer glove for fine motor tasks and still have a little degree of protection with just the liner.
When I was set up stagnant in a hide sight or on the range, I wore my glove liners under a pair of convertible mittens. That way my hands were insulated, but I could always just pop my trigger finger (or all of them) out to take a shot or manipulate gear.
As for cold weather related glove brands, I like Serius and have owned several models of their gloves for everything from military stuff to skiing and hiking. I always still wore my glove liners under them which I guess helped increase their warmth rating.
