I'm late, but I'd like to add to the discussion!
I love wearing speedos because I enjoy swimming laps. I love how unrestricted my legs are to kick in the water. Even in jammers, I always felt a little held back by the longer legs of the suit. It was partially due to the amount of tight-fitting fabric and partially due to a mental/subconscious restriction; I was always afraid of stretching the fabric and either making my suit slip down during a flip turn to reveal the top of my butt crack or over-stretching it and tearing a seam.
Also, briefs allow the water to pass over my skin and leg hair, and the sensation is wonderful; it makes me feel as fast as a pro swimmer! Though I am, of course, completely NOT as fast lol.
And then, the feeling when you get out of the pool and lay out in the sun and feel its rays warm your entire body, including the thighs which are almost always covered for the rest of your day, is absolutely wonderful!