I dunno, personally, Kapono is a very good team defender while Moon is more of a solid one on one/help defender due to his athleticism.
However, if our offense is running from the low blocks out, I'd be more inclined to run out Kapono out there. If anyone decides to double one of the bigs, you kick out to Kapono who you know has a good chance at hitting open jumpers (see his Miami stats). If you trot out Moon there and seeing as he's an average shooter teams would be willing to let him and try the open jumper. With Kapono and Parker and Calderon, teams really can't afford to cheat off one of those guys.
Plus, if Ukic plays uptempo, plus Hassan, throw out Moon out there you have a pretty atheltic second unit that shows the other team a completely different set of players and now the opposing team has to match up bascially for a completely different team. We're not simply plugging in and playing the same system, but we can potentially play an entirely different game. It would drive opposing teams insane, because how do you adapt?