Almost always boxer briefs. With most of my dress slacks, the leg of the boxerbriefs will print on the thinner fabric so I'll have to wear briefs, but otherwise the boxerbriefs.
And, I've gotta say that I'm always a little fascinated by the guys on here who fetishize people gawking at their dick. As in, the notion of a guy with a big dick freeballing, snaking it down the leg of his trousers, etc. Perhaps where I grew up everyone was more conservative than yall, but even the general bulge made by wearing more constrictive underwear provided enough notice to be uncomfortable. Someone walking by and actually being able to make out your tackle would feel almost obscene, like you're just walking around naked (though I know that idea is fetishized as well...).