I wear briefs most of the time. I have tried trunks or boxer-briefs or whtever they're called, but I didn't like how they hung onto and constricted my ass and thighs (I'm not the slimmest guy around, either...). So breifs keep the boys in check (I have a short fuse, if you know what I mean...) and, provided they're not too tight, are fairly comfortable.
I have actually been trying boxers as well lately, and I rather like them. There is much more freedom, and they're quite comfortable as well, so I think I'll extend the trial...
And I do occaisionally freeball, except that after a while it begins to hurt. I need a bit of support.
It all depends on what I'm wearing, where I'm going, and who I'm seeing that day...