Well, this may not directly address your question, as far as one excursion vs. another, but...
I highly recommend going to Trunk Bay on your own!
1. It's cheaper.
2. You are on your own time schedule.
You can save a substantial amount of $$ by going there on your own, and it's easy. Then you are not at the mercy of the other people on the excursion, and you can do things your own way, in your own time. We ( a family of 4) did this for about $120. The Disney excursion would have been twice that! With 8 people in your party, you could save even more. All you need to remember is to get back to the ship on time!!
When you get off the ship in St. Thomas, there will be taxis lined up to take you anywhere you want to go. Take one to Red Hook, which is where you catch the ferry. Take a ferry from Red Hook to St. John, then another taxi to Trunk Bay. It's that easy!
It's easy, however it is time consuming, so I suggest leaving as early as you can in the morning. Then you will have more snorkeling time, and still get back in time to shop in St. Thomas!
'Beano'
