Yuffie outsmarts the entire party during the entire Wutai sidequest!

From a fighting point of view she has one of the best limit breaks (Doom of the Living is probably the 4th best), she's got the best Ultimate weapon and all her attacks are long range! Win, win, win!

Plus she's an attractive young nimble barely-legal ninja who's unbuttoned shorts suggest she's a party gal. She isn't needy like Tifa or as forward as Aeris. Cloud you're a fool! Fool!