Smartwool socks seem to be universally endorsed among experienced winter cyclists. The New Zealand merino wool used in Smartwool socks is extremely comfy, the socks are reasonably priced and the company is based here in Colorado.
I own several pairs of Smartwool socks and I also recommended Smartwool socks enthusiastically. In the summer, I hike and climb mountains wearing these socks. In the winter, I hike, snowshoe, and ride my bike in these Smartwool hiking socks.
The two bottom photos to the left shows two pairs of my Smartwool hiking socks after two years of this use.
Eventually, I asked the local hiking shop for socks that won't fall apart on me. They recommended Bridgedale Socks. I bought the Trekker from them, a midweight sock similar to my Smartwool socks made of merino wool designed for trail running, hiking and backpacking. After two years of use, my Bridgedale socks have held up significantly better than my Smartwool socks. There is no hint of sagging in the cuffs. The socks fit my feet better, meaning there don't blister like I do with the Smartwool socks on my peak bagging runs (the discolored areas on the Smartwool socks are blood stains).
Because they're made of the same Merino wool as Smartwools, the fabric is just as comfortable. The Bridgedale's are a little bit pricier but the construction and quality are significantly better.
The top photo shows a Bridgedale Trekker sock after two years of use similar to what I've done with the Smartwool socks. There's absolutely no thinning and the sock fits just as perfectly as when I first bought them.
I currently own two pair of Bridgedale Trekker socks and I'll buy more in the near future. I now enthusiastically recommend Bridgedales to anyone who asks.