Online game = Dumb. What, would everyone be keyblade masters and you travel to worlds and beat heartless, and thats it? Most online RPG's don't have plots, and are just good for going around and killing things, but KH is one of those games where it needs a plot and a storyline otherwise, it would be boring.
T.V show = It's an ok idea so long as it doenst end up like the Legend of Zelda T.V show... watching that made me throw up...
Movie = Definately the best idea out of the three, because theres less chance of them ruining it because it isn't a longterm T.V show, and plus Kingodm hearts would be awesome in CGI (I'm assuming it would be a CGI movie)
I mean, just look at ASAS and DD, they were awesome, so imagine a whole movie as awesome as that. But it would have to be about Sora, adn the rest of the gang, instead of something that just uses the Kingdom Hearts label, but doesn't have anything to do with the actual game besides the fact that it has heartless and keyblades...