In Grand Cayman, Stingray City is a must if you have never done it. We went for a second time 2 months ago and had a great time. We booked with www.grandcaymancruiseexcursions.com
We went on the Buccaneer Stingray City Catamaran Excursion. It is one of the few that has 3 snorkeling stops. The price was only $39 per person and the crew were great. Also, we only had 12 to 14 people total on this excursion.
Booking through the ship costs more and there were a lot more people.