I look for as high a percentage as I can find. Found some good deals at walmart. 88% merino. Very warm and surprisingly dry.

I tried the new Alpaca socks. they work well. but I still double up with a thin pair and then the Alpaca. But at times they are too warm and start to sweat. that's when the cold sets in. So, I did get a pair of remote control battery operated socks of Amazon. They worked great and are not expensive at all. Once the cold sets in you turn them on. Then off again by the remote in your pocket. Great for duck hunting. If you leave them on, you get about 3-4 hours at full heat. There are settings on the remote for low, med, high.