I have 3 or 4 different species of hermits scuttling about my tank and as far as function goes the scarletts are my favorite but they're almost entirely nocturnal so I never see them. My favorite as far as form and function is my Halloween hermit. Sure its a bit of a wrecking ball but it's very pretty, always out on display, and a veritable vacuum cleaner. My other indispensable reef cleaner is the money cowery, these are certainly nocturnal but clean a silly amount of algae every night.