I think several outfitters in the Caymans do a good job. You can check their ratings on trip advisor. We used a new company called Reeleseacharters. They were expensive because they only took us, so it was a very individualized trip. I have heard great things about Capt. Marvins and a few others as well.
Just make sure they have a money back clause if the ship doesn't dock since it sometimes doesn't at the Caymans due to tendering and rough seas!