I've given up on knee socks as knee socks; my calves are apparently too large. Or at least, when I can get the socks all the way up to my knee, there's definitely a constriction of blood flow. So I tend to stick to shorter socks, but not the absolute tiny short ones, when have a tendency to slide down my heel and into my shoe. Oh, and I can't stand tube socks for some reason.

I have a variety of socks ranging from sport to more interesting, plus plain black. Since I mostly wear skirts, I figure socks mostly don't look right anyway, so I can play around. I still tend to match the fun ones to my outfit when I wear them.

Oh, and I don't care about thickness, particularly, though I know that thin ones will wear out faster and thick ones may be cushier on the feet (but all the fun patterns are on thin ones).