The one 3-star that stands out to me is probably Marigold because of her battle skill (shared with the 4-star Hibiscus) which hits for 3 instances of damage. This makes her one of the best at killing the enemies that only take 1 damage from everything. Most of them now are harmless (bonus stage bosses) or you don't want to kill them too fast (seed bearer), but they might introduce more dangerous ones eventually.