I switched from Smartwool to Bass Pro's Redhead brand, with the lifetime warranty. There's a Bass Pro Shop within 50 miles, the two pairs I have fit better than Smartwools, and if I wear them out, I can take them in and get them replaced, free. They were on sale for about $10/pr., too, when I bought mine.
(I did live within 10 miles of the BPS, but moved recently.)
Frankly, I like the Redheads better, but both brands keep my feet warm. I wear nylon dress socks under them, but they aren't really needed.
I take blood pressure medicine, and my feet get cold pretty easily at times. Not an issue with the Redheads, though.
