Hannah adores dandelions because you can make wishes on them! And they're so pretty when the seeds are floating through the sky. And they're pretty when they're all cheery and yellow. AND as weeds, they're underappreciated, so somebody needs to love them!
Alicia isn't too picky. But she prefers fake flowers, because the real ones are such a bother to keep alive when they're not even going to last very long.
Cho likes water lilies because she thinks flowers look better juxtaposed against water than grass or dirt. She also has a soft spot for hyacinths for no special reason.