I chose Aeris for her tragic story, her innocence and her inner wisdom. However, Vincent my dear Valentine is just dark, powerful and damn gorgeous. (I can't wait for DoC!)
I can't say I like Tifa very much. She always seemed like a lost spirit who couldn't do anything without her hero to save her. I don't like damsel in distress types. At least Aeris was a martyr and died nobly.
Sephiroth? Ok, I'm one of the bad evil fan girls on this one!