The best thing about the Brazilian square cut swimwear (
sungas) is their roominess and comfort.
On the beaches in Rio, super hung guys, straight and gay alike, walk around and casually and absently play and grope their junk, easily shifting themselves from side to side.
One caution: you need a fairly flat stomach for these puppies, like low hung jeans. If you have a little belly and still want to wear something small, you might want to stick with the traditional speedo.
Here's one of my prime lust objects and a fellow LPSGer modelling a great square cut:
http://www.lpsg.org/gallery/showphoto.php?photo=30005