I don’t care about fashion. I don’t even percieve anything to do with fashion in men’s underwear, since I almost never see men’s underwear. I buy underwear by habit, and comfort. No one sees my underwear but me, and I don’t see them on myself all that often, since I don’t check them out in the mirror while getting dressed.
A woman wearing underwear that were obviously chosen to look sexy doesn’t look sexy because of the underwear, but rather because she chooses to look sexy. If she thinks her underwear doesn’t look sexy, and she wants to look sexy, she should try taking them off.
I wear briefs (colored) during the day and find boxers perfect for bed. Generally the same reasons many have given - during the day I don’t want a lot of shifting of my equipment while in bed it is good to have “room to maneuver”.
Based on unavoidable observations at the gym, I would say that the preferences of men in my area are split into roughly thirds for briefs, boxers, or boxer briefs.