Like so many others here, it's briefs and boxer-briefs for me. I like things to be under control and supported "down there." I do have some regular boxers that my wife bought for me long ago, and if the laundry has piled up, I'll occasionally dip into those--and then be uncomfortable and shifty throughout the day.
I sort of equate wearing boxers as a man to going bra-less as a woman. Stuff's just sorta hangin'. Social aspects aside, allowing part of one's body to be forever lagging the rest by a second or two is a bit disconcerting. My math teacher in junior high had an enormous tripple chin that obscured the whole front of her neck and was like a two-second window into the past. I don't think we have any garments designed to solve that one, though.