1) Sephiroth was my favorite character. Maybe it's because of the uniform.
2) Vivi was not the most powerful sorcerer in the whole series, but despite his youth, he still kicked some butt. Favorite scene was his challenge against the Waltz.
3)Terra was unsure of herself for most of Final Fantasy VI, but she was more commanding and far more powerful when she took on Esper form.
4)Faris was a pirate who disguised herself as a man. She took little crap from people and had fun being a pirate leader than to join the royalty she was born from.
5)Beatrix could arguably be one of the toughest powerhouses. She took "your" whole team alone in so late in the game, which I can't think any other "designated villain" could do. She was honorable, strong, but still had a soft side to her.
6)Sabin was a powerhorse. A strong martial artist and frightfully powerful. He gave up a place in his kingdom to attune his body and enough moves to give even Akuma a workout.