For some reason, I was musing over Final Fantasy VI a few weeks back, and I was pondering about what sets it apart. I (sort of) came to the same conclusion as Silver Prime in that there isn't a "head honcho"; however, he seems to suggest that it is a bad thing, but I think it's what truly sets the game apart... in a good way. Arguably, the game does focus the most on Terra as the unraveling mystery directly involves her, but I think that tends to mask the other characters' growth throughout the game. Albeit, that also tends to focus on a much more select few (Locke, Celes, Edgar, etc.) rather than every single character -- sorry, Umaro!
I think that's what made the game interesting. The other characters didn't feel like they were only there to prop up the main story, but rather they also had their own experiences. In some games, the character just leaves your party, experiences growth, and comes back (e.g. Rydia in Final Fantasy IV), but in Final Fantasy VI, you typically play as the character for their story bits.