BY FAR! She is the smartest!

It was between belle, mulan, jasmine, and pocahontas.

Thanks to Mulan's intellegence and ability to think fast and take the right decisions, she managed to win the war and save China. Belle is not even half as smart as her in my opinion, because while she indeed liked to read a lot and embraced a pleasent influence of self education, she mainly read C class romantic novels ala Twilight and re-read that stuff for 3 times. It doesn't make her stupid or smart, but it doesn't add her bonus points either.

Alright, almost said Belle, but maryksand has convinced me. Now that I think about it, I was always disappointed in how Belle never seemed very smart at all after leaving her little hick village. "Oh, is this the West Wing that I'm not supposed to enter under any circumstance? Could this be at all in direct risk to my life...? NAH, BRO, LET'S WALK TOWARDS IT."