Actually, I should expand on this a little, since it’s apparently a question of world import.
Boxers are for grown-ass men. Briefs are for boys and Southern European gigolos.
I don’t even know why we should regard this as a serious question, except we live in profoundly unserious times, when people who’ve reached the age of majority no longer wish to act as if they’ve become adults.
Personally, I regard the day I stopped wearing briefs and started wearing boxers as being one of the major landmarks on the road to adulthood, on a par with getting my drivers license at 16, and having my first legal drink at 21. It happened the summer between junior high and high school, when I demanded my mother go to K-Mart and buy me some boxers, so that I would not have to be seen wearing tighty-whiteys as I changed for football practice. In my teenaged clique, in 1976, boxers were a symbol of manhood.
Otherwise, except to say that boxers are a)for grown-ass men, b)should be made of cotton, c)in either a festive plaid or a solid color (blue, white, or military green only), I have few opinions about underclothing for men. Pick your style of underwear (as long as it’s boxers) and stick to it for the rest of your life.
Underwear is simple. I hate those online underwear stores (like this one Vocla) that treat underwear shopping like it’s bellying up to a smorgasbord of butt-hugging, nut-hugging styles. It’s all briefs and tight boxers, in a profusion of colors and cuts. Although, judging by the photos of the models it’s clear I, a middle age straight man of conservative tastes, am not their target audience.
So, to conclude: