I have read about several different types of snorkling -- lagoon, drift, stingrays and coral gardens. We are on the 7 day cruise in September and will only be on Moorea and Bora Bora for either shore excursions or private tours. Any suggestions as to where we will be best off for any of the above tours and whether the PG tours are worthwhile or whether there are private tours that are recommended instead. Thanks.