My お気に入り アニメ school uniform definitely has to be from The Melancholy of Haruhi Suzumiya and both the boys & girls because they both aren't all that plain,they both look really nice the way they look and I mainly mean the Long Sleeved & Even the Disappearance of Haruhi Suzumiya uniforms so they're my お気に入り currently.
The uniforms in Azumanga Daioh. But really the only reason is that it's my お気に入り アニメ that takes place mostly in a school and when I see it, I think "Azumanga Daioh!" School uniforms all look the same to me and I don't really take note of them.