We rented a private charter for the four of us ($400 US) with Cayman Outrage Ecotours. We got to Stingray City before anyone else (My parents did not get in the water due to difficulty getting on/off the boat (would have been the same for any boat), and our guide, John Michael, was knowledgeable and helpful.
He took us to a private beach, where we all waded on the sand bar and looked for shells, etc, and then we return home through the Mangrove channels. He talked just enough to make it interesting, and give us information, but also let us just enjoy the view.
We walked through Georgetown a bit, but the shops all seemed to look the same. However, it was MUCH better than Jamaica and I can see returning to the Caymans someday.
The local vendors have the potential to make this very unpleasant. Even sitting at a resaurant, a guy was wading in our water-view trying to sell us things. That said, I think if you go with a tour, you will be very pleased. We went to Mystic Mountain for the bobsled, zip line. It was pricey, but if you take your swimwear/towel, you could make a full day (4-5 hours) of it. My parent used Traverse Jamaica Tour group to see the White River and one of the plantation homes, and said they really liked the White River.