My str8 friends are split down the middle, half wear boxers/free-ball (most just wear the boxers so they can show the waist band lol) and the other half wear briefs. All of the Bi guys i know wear boxer-briefs, and i own and wear everything except a thong.
boxerbriefs look the best but they're a nightmare with tight 501s, they tend to grab onto other fabrics and get jumbled around, where smooth boxers dont, and anyway i prefer commando above all underwear.
i like the boxer briefs. or "trunks" if one wants - they're more comfortable because the legs aren't nearly as long, but they're not breif-short. i like boxers, too. but i like them to fight tighter- mostly because of the thing about puting on jeans and having the legs ride all the way up when you pull your pants up.