Like clockwork, the busty girl is evil, the one with the "medium 'premium'" is idealized.
The designs follow this playbook as well: the evil boobs have short hair (read the end of CubexCursedxCurious to see what happens to a girl, Muramasa Konoha, who looks like the "medium premium" in this story but competes with a loli--she gets rejected and cuts her hair for Character Development™), while the other one has an otherwise beautiful appearance--long hair, softer eyes, and even wears glasses.