Coolest outfit: Beatrix's, it's elegant and feminine, and looks pretty comfortable to move in as she fights.
Most practical outfit: I'm partial to Ingus's freelancer outfit. It's simple, yet it has some pieces of armour for protection.
Most boring outfit: FFI Black Belt's outfit. Practical for a martial artist, maybe, but oh so plain...
Most impractical outfit: I'm hesitating between Lulu's (if only because I'm... er... sharing some of her assets, and I've worn a corset before and I almost suffocated without even MOVING around) and X-2 Rikku's, too frilly and bright for a thief.
Best formal outfit: Celes's opera gown. 'Nuff said.
Best uniform: SeeD uniform, agreed.