This question stumped me for a while because all uniforms sort of blend together for me as just another seifuku or gakuran or blazer set or whatever. If I had to pick a favorite, it's probably the student council uniforms from Shinshi Doumei Cross! They're individually tailored to suit each council member, which is pretty neat. I also like the black/white design because it's really striking.

Aiden and I have also agreed that Ouran, despite being one of the most glamorous anime schools, has quite possibly some of the least flattering uniforms ever. Those bright yellow poofy dresses... why.