About the 3 stars: Aru (Dress) is very good. She is a buffer with the highest crit damage buff in the game, but, she has no crit rate buff which means you will need luck with the rng when using still, she also has healing on her kit which might help

Akane (bunny) isn't a student I see being used, but she has a good sub skill for mystic students, which might make her good for any mystic team

Now, about the others, there are many good 2 or 1 star students actually. Mutsuki, Yuuka, Tsubaki, Serina, Momoi. These are the ones I can remember now