How long ago was "day one?"
I agree that the porcelains are your best bet. They aren't going to fight w/ a clown over an anemone like an anemone crab (and anemone crabs will make a bee-line for any anemone, which ****es off resident clowns!) I haven't had problems w/ small emerald crabs, but they can get a bit grumpy when they grow, as well.
The sally lightfoot is known to change its diet as it grows, so do be careful.