The answer is wool.

All the time. Even in the hot weather. Hear me out:

First: Why Wool Socks?

Wool doesn't itch: Specifically merino wool doesn't itch, so you can abandon those concerns.
Wool doesn't wet. Since Wool doesn't absorb water very well (like cotton), your feet stay drier should you walk in the rain, or through a puddle, or if your feet sweat.
Wool dries quicker. Wool "wicks and breathes" like a high-tech synthetic material (and again, unlike cotton) it dries out easier. (That also means a thin layer of wool is COOLER than a thin layer of cotton if there is any moisture involved.)
Wool has natural properties that make it "anti-stink." So:
1. fewer worries about stinky feet when you visit a "no shoes" destination
2. for travel and camping, the lack of feet stink is a big bonus: you can wear your socks twice (or more) without grossing yourself AND you won't contaminate other gear with feet stink
3. if you're tight on laundry, wool socks can be worn again without too many negative circumstances. (Some folks even wear them twice routinely, as a matter of economy and sustainability.)
You've heard of three-layer clothing systems being superior, right? (And we're not just talking about camping.) Well, how come you're not applying that logic to your feet? (Wool socks make sense in this context because 1) they function as a base layer and 2) they don't stink like synthetics.)

You want merino wool.
You want as close to 100% wool as possible—and do read the label, because a surprising number of socks advertised as "wool" have a tiny amount of wool in them. (Again, when reading the ingredients, you want merino wool to be specified on the label.)
Since wool has a reputation for being warm, some people think that varying the percentage of wool in your socks is the best way to ensure that your feet don't get hot. NOT RECOMMENDED. Instead, buy thinner socks for warm weather and thicker socks for cold weather. Always look for as close to 100% merino wool as you can get.
Smartwool is honestly the only truly reliable choice I've found, though many people swear by Darn Tough.
I tend to buy a size larger than my official size, but part of that is because I often put my wool socks in the dryer.