Merino wool all the way! Fox River is a great US company, I had a quality control issue with some socks I bought from them, one e-mail and they took care of the issue. Check out REI as well, 100% guarantee there as well. Some like a poly liner underneath, personally, I don't. Make sure your boots don't constrict your feet, poor circulation is the biggest reason for cold feet. If your feet are getting cold while on stand, either in a tree or blind, you might also consider bringing a dry pair to change into once there. Your feet will sweat and get damp on the hike in, once they're damp, you'll never keep them warm if sitting. Putting on a dry pair will make a world of difference. One other trick is to spray your feet with unscented anti-perspirant before heading out, it keeps them from sweating as much, therefore your feet don't get cold as fast.