Brian Kinney is an advertising executive, cocky, brash, slutty, and with a dick renowned for both its size and beauty.
Gale Harold is an actor quite a few years older than Brian, shy, not into his looks or the limelight, with what has been said to be a modest endowment at best, although I have no real idea if that's true or not.
Justin Taylor is a cute young thing with a gorgeous ass and a pretty big cock (direct quote), but not as big as Brian's.
Randy Harrison is an actor quite a few years older than Justin, with a very different outlook on life, and a really nice ass and a dick that seems to be just about the exact same size as Justin's... thus, smaller than Brian's, but bigger than Gale's.