Hmm Iunno, there's quite a few well dressed characters in Touhou.
Yukari immediately comes to mind, her dress is pretty fanceh.
I really like Byakuren's outfit as well, especially her bamboo hat in the fighting games.
Ichirin's pretty well dressed as well, I really like her hood.
Alice is pretty classy.
Lastly, I really like Sakuya's maid uniform :3.