Wish I could say that I go commando, but the feeling is still just too weird for me. I've tried it before, and can manage with track pants or whatever, but with any seamed pants or especially jeans it just ain't gonna work.
I often don't wear underwear, especially when wearing loose trousers or jeans. There is little rubbing/chafing, and getting aroused isn't an issue. When I do wear underwear, I wear loose boxer briefs.
I've stopped wearing underwear and shoes everywhere I go except school where I have a uniform that makes chafing a problem and it requires work boots. It's quite enjoyable.
I do both. If I wear underwear, it's either waffle-knit long underwear (amazingly warm, awesome stuff) or soft loose-fit knit boxers. I do wear boxers more than I would if my jeans where in better shape. As it is, a lot of the jeans I wear daily would get me arrested for indecent exposure without boxers.