This has nothing to do with personality, this is all about game mechanics and so the question is, who is the games best character?
I'm going to have to give it to Rydia in most of the versions but for the DS version its Cecil by a long shot since he can take advantage of the Augments way better and becomes a powerhouse early on.
Rydia is just great cause her offensive magic is wonderful and once you get her high powered summons, she makes dungeon crawling a breeze and is a formidable enemy in boss fights. Its a shame she been nerfed in the DS version with her summons having longer cast times and costing more MP.
Kain gets an honorable mention as well cause his simple design is lethal. its just a shame he spends most of the game brainwashed.