Smart wool/Merino wool underwear. I got a single pair about 7 months ago and they've been my favorite meaning they get worn about 1/2 the time. (I know... too much info!)
I don't have experience with them in the cold (live in Malaysia where it's hot and humid) but they seem great in hot, humid weather. My favorite before was ex-officio's synthetic boxers. I wear them for riding, hiking, anything... often my jungle rides include miles of hot, sweaty work on foot, hiking hills building bamboo bridges.
They stay wet longer than ex-officio synthetics BUT they are more comfortable to wear wet. (Of course I'd rather have any dry pair than a wet pair but they are the most comfortable wet and any dry pair quickly become wet in the jungle!)
They dry faster than cotton but not as fast as the synthetic ex oficios.
You'll get chaffing anytime you run/hike miles in a wet underwear BUT these are the best in that situation in my experience.
They feel the coolest in hot weather between synthetic, cotton and wool.
They do wear out faster and are expensive.