Hi S.,
Forgive me if I'm overstepping here....I don't think you should predicate your daughter's education on what she will be wearing. I'm assuming this is one consideration out of several that are driving your decision making process.
That said, I love the idea of uniforms, especially in middle school. children, especially hormone raging ones, can be cruel to each other and what they're wearing, or not in some cases, is a really easy and sensitive target. It levels the playing field and gives them even more of a chance to focus on what they need to focus on at school....getting their education.
My son goes to a private school and they do not have uniforms. however, it's a building filled with pocket protectors and glasses held together with adhesive tape so no one ever seems to notice clothing....heck a lot of them look like they're still in their PJs. And what's up with teenaged boys leaving the house in single digit weather wearing T-shirts and shorts??? Queue my Seinfeld "what's the deal" moment....sorry for the digression.