In response to Del's comment about VI doing a better job at not leaving characters behind, I find that true but there is a reason for it.
The game isn't really about one person going after something. IX was, at it's core, Zidane's story and him going out to save the world. In these stories, other people getting left behind plot wise happens, though really good story telling still keeps them all relevant and keeps you caring about them, which IX does a fine job at for the most part.
In the case of VI, it does start off with Terra running from the empire and the whole half esper thing, but really that is but a minor part of the actual story. It's people from all over the world rising up together to fight against the empire. The overall story isn't about any one character, but specifically about the group itself and it's struggles as a whole. They do give everyone their moments to shine which I greatly enjoyed.
I mean when you get down to it though, this story is just as much about the struggles of Banon and Cid as it is Terra and Edgar.