For me, definitely Leanne. I mean, Reyson's cool and all, but Leanne is one of my favorite characters in the game.
Granted, she speaks the Ancient Tongue, and this makes it hard for people to know her personality. However, the Ancient Tongue can be translated directly into Roman text, so it is possible to understand what she says. This adds a whole new level of depth to her character. When she speaks her own language, the reader only recognizes a pristine heron speaking a language more ancient than the Common Tongue. She becomes 2D, imbued with an unrelatable wisdom and lost magic (Seid). However, if you can read what she says, you realize that she's really just a simple and really sweet girl. Having taken the time to translate her speech, I've become a big fan of hers. Besides, the pairing with Naesala is great.
Rafiel's sprite is cool-looking, but I'm not a big fan of his character art.