I get Terra's. She's sorrowful. The weight of the world shows upon that beautiful face.

I think Eiko's sums up her inner character. Her bright and spiritual one. (Minus her annoying side)

Yuffie's sums up her cheeky character.

You're so right about Cloud. Have you ever looked at his portrait in the flashback? He looks more sweet and innocent then.

Zidane definitely has mischief written behind that smile. But, like Yuffie he's of the thief class so its expected.

And remember that Garnet's changes. I prefer her first one where she looks all demure. She doesn't suit shorter hair.