Mia was always really weak for me. She was great in all the other areas, but she couldn't kill very well, so I dumped her next playthrough and used Zihark. As I expected, he was much better than Mia in the strength department, which led me to use him over her. Made quite a great Swordmaster.
Stefan was also very awesome, particularly his story and character. His stats aren't bad either, considering he's a pre-promote. Lucia is...eh. I like her character and design, but she fails as a unit.
Kinda stuck between Stefan and Zihark...