Hmm, Terra? Although she wasn't a 'lead' like Lightning.
I would hardly call Terra flirtatious, lol. And arguably, Celes shares the female lead with her.
Serah doesn't really fit quite with what I have in mind. I consider Serah a great character and I think she's strong willed and adorable, but she still needs to be rescued and protected. Not that there's anything wrong with that, but Lightning was more independant and didn't have a guy around her a lot of the time. I would like that aspect applied to a more in depth character. Like someone mentioned Light is very one dimensional, and it seems like the character design is 'trying too hard'. To be honest, Lightning gives me the same feeling as the new Dante design does for DMC in a way. The character design is just plain trying too hard to be badass, and it shows. That's just my opinion though.
I think I'd like to see more of a character like Beatrix who was a stunning beauty, but a deadly killer. She was really regal, and her attitude in general was perfect. She was cold, but she did care. She even had that romantic side to her too. A lot of people loved her and were disappointed she was more of a minor character. I would love to see a main like her. *^*