Master Riku, that still sounds weird since playing KH and CoM again but It'd probably be him because he really earned it after changing so drastically since the first game.
Soon enough they are going to run out of Disney films they can actually use and aren't just the same thing over and over. They then might add rehashes of old worlds, more FF worlds or even go into the realms of things owned by Disney (Star Wars and Marvel...hopefully not) and before the whole series becomes stale.
That will be a sad day though...
I didn't mind it, it wasn't my favourite of the 3D worlds, that honor belongs to the additions to Traverse Town. It was still a well planned out and nice addition to the repertoire of Disney Worlds.
I'd like to see the reappearance of Atlantica in future titles, It's a pretty famous and popular Disney Classic, it makes sense to add it again, just like the several reappearances of Olympus Coliseum and Agrabah.
It's probably going to be Aqua because her playstyle matches mine, using magic is my usual main since KH with Aero and KHII with Reflect.
Ven would be a close second though because he's got amazing moves and he is pretty balanced compared to the other two.