Neither really. What you really want is relaxed or loose fitting pants, one size larger than you would normally wear. This will allow for the pants to still fit loosely. It helps if you wear pleated slacks too. This will visually break up the area around your diaper area.
Also, wear an extra long shirt. Tuck it in, but then pull it back up some. This will keep the shirt loosely draped over your belt line, which will add to visually breaking up that area even more. Lastly, always bear black pants. The black will hide any potential leaks. And no diaper is more obvious than a thin one that has leaked.