Well I'll have to disagree to some posts here. I spend most days in heavy weight socks. up until I changed jobs a few years back, I was outside as much as inside during the winter and wet over half the time, or either hunting or standing in a barely above freezing river somewhere chasing salmon/trout/grayling in the 'summer'.
That said.....
smartwool is a great, very warm sock. I wear the mountianeering (red), which are the heaviest they have. It's warm very very warm! if your feet sweat, spray them with deodorant first.
my socks wouldn't get close to 10 years before I could see the mesh the wool is woven on, the pile was gone or severely reduced. Every fall I buy 4 or 5 pairs for hunting season most years so I have half a dresser full of them. I'm not trying to talk you out of them, just that YMMV depending how often you wear them, how well they wear. My older pairs I wear around the house/shop etc. But that pile on smart wools will fall apart.
I currently work in a power plant these days. Another local T-ganger put me onto Darn Tuffs. They are too warm as well for me to wear in a heated plant and I unfortunately lost my cold weather acclimation as well grrrr, something about being wet and outside through the peak cold of winter vs staying inside working by hot boilers changes things haha. When I do wear them here my feet rot! They're just too warm! I do wear them turkey hunting down south in the spring and are my go to's when it does get warmer up her during the summers while I'm out chasing fish.
If you go with darn tuffs I like the heavier kind of dark green model. buy one size larger than you think you need. If, I should say WHEN, they shrink, if you're snug to begin with, they'll be too tight for a cold weather sock!!!! Every pair I have shrunk just enough. I picked up some lighter pairs for wearing during earlier season hunts and was glad I did...my sheep boots shrunk and I wasn't able to wear my typical heavy socks (smart wool). The pairs that shrunk didn't shrink much as I cant tell which is which visibly. But my feet will freeze in a heated building, which is the dead give away!
Darn tuffs have a lifetime warranty as well! Just heed the size warning!!! If you don't your feet WILL freeze!