I've always worn briefs because I like the support. I suppose the boxer-briefs would be comfortable. I wear the spandex compression stuff under my shorts during sports because the compression helps keep my thighs/hamstrings from tightening up.

However, on a normal daily-wear, I don't think I'd like them. I always feel like it's a little too hot anyway. Always, everywhere. I'm in shorts and a t-shirt and about to break into a sweat while others are huddled in fur parkas. Boxer briefs would just add to the problem.