Tough choice. I can narrow it down a bit, but I don't think I can really pick a favorite.

Auron is the first to come to mind. Quiet, badass, and unlike the other quiet badass types, not a brooding emo kid. He's a man of age and experience, and born from the two, wisdom. He's one of the smartest protagonists in Final Fantasy history, having gained knowledge from his journey as a guardian, and more from his journey to another world, and more still from living on after death. The keeper of secrets role also earns some points from me, as I'm a man who values knowledge, and seeks mystery. He's the perfect character to fill the mentor role in the hero's story.

Beatrix is another favorite. The whole story of her conflicting feelings about her oath to serve, and her clear awareness of the wrongness of what she was being asked to do made for a complex character. She kinda had the whole Cecil thing going with seeking redemption for past sins, but was just more awesome while doing it. And I always find the massively overpowered solitary warrior characters interesting. Also bonus points for being a female who uses white magic, and unlike all the other white magic using females, NOT being a pansy hiding in the back row providing support, but instead being the front row powerhouse with an attitude.

Zack Fair, one whom if I had to choose right now, would probably be my top pick for favorite. Unlike other protagonists in the series, he hasn't been some conflicted tortured soul seeking himself. Zack had total clarity of purpose at all times. He was a man who fought for his dreams. He was unfailingly loyal to his friends, risking his own life to save others without a second thought. While other protagonist relied on the strength of their friends to accomplish anything, Zack carried he weight of his world all by himself, and did so with a smile on his face. His strength of character was unmatched by anyone else in the final fantasy universe.

Sephiroth, another top pick. As villains go, Sephiroth is definitely my favorite. Cold, calculating, manipulative, ruthless, and knows just how to get under someone's skin. In addition to his character being perfectly suited to villainy, he had something other villains usually didn't. Real power. Most other obtained power through manipulation, or some twisted plot, but Sephiroth already had power. He didn't have to lie or go behind people's backs to get where he got. If he wanted something, it was his. He had no qualms with breaking into the highest security building on the planet to take something he wanted, and he killed anyone stupid enough to get in his way.

Kefka Palazzo, while not my favorite villain by any means, there's something you jut have to love about a psychopathic homicidal clown.