I prefer a Heartless over Riku simply cause the devs can use more creativity making a moveset for a Heartless than Riku. A Heartless with powers based on the other types of Heartless would makes for an interesting moveset(think Chibi-Robo) than anyone playable 'cause everyone playable plays the exact same way as Sora. I live with a two sisters who are borderlining obsessed with Kingdom Hearts(one of them well past that),and because of this I've been forced to play every single KH game ever made(God forbid when 2.5 comes in the mail ). They can change Riku's specials, but in the end he'd play almost exactly like Sora and would essentially be a simi-clone to Sora; which the devs want/should stray as far away from as possible. Of course this is just my opinion.