We used Native Way watersports a year ago. They have 2 different choices. We did the one that goes to stingray city, coral gardens snorkeling, and starfish snorkeling. I chose that one after a lot of research on cruise critic. We were very happy with them. The boat was large but not huge, nothing like the size the cruise ships use. We probably had about 50 people aboard whereas the cruise ship excursion boats had hundreds. The boat was immaculate and with three guys aboard the service was great. There was lots of help for beginning snorkelers. In stingray city they make sure everyone gets a chance to pet, kiss, pose with the stingrays. It was supposed to be $120 for the four of us (2adults & 2 kids), but once onboard it was only $100. An amazing bargain compared to what the ships charge. Afterwards they dropped us off where ever we requested. We went to a nice spot on 7 mile beach. The owners name is Sharon Ebanks. You can email her thru her website with any questions, and make reservations thru the website. We loved them and highly recommend them.
After our first cruise, we only have only done excursions on our own, and have never been dissappointed, unlike our experience with our Carnival excursions.
Whatever you decide to do, enjoy Cayman, it's great.