I think that aragamax (aragonite based) sand would be best. It's personaly preference as to grain size. Some like fine others prefer more course.
Either way, I think avoiding some of the temptations associated with the cost savings of bulk play sand is a good thing when starting a reef tank. Saving a hundred bucks now can cause massive headaches down the line when a complete removal of an established bed is the only option to ending nuisance algae.