Any that fit in my locker, can hold all of my homework, and has enough room for my vest/jacket/street clothes.

It might sound like a no brainer, but a few times I've had an issue with one of each. Sometimes they rip because the books are heavy or are too small to neatly hold non-uniform clothes (or uniform clothes when not at school) or don't fit in the locker when they're any bigger than that.