Do you mean what is best for coral? I’m not sure that coral prefers anything. It is your live rock that is important for that. Personally from what I have researched I would just stick to stuff like agra—alive. It’s the basic live sand that is an all around good sand. “Regular Sand†I’m guessing that you meant as “Pool Sand†or “Play Sand†is not good for marine tanks. You need sand that can buffer the pH to a suitable level.