We also booked through Captain Bryans and Captain Marvins and went on the new Buccaneer Catamaran. We were lucky because the day that we were in GC everyone on the ship got a 7am wake up call advising everyone who had booked the excursion through the boat would not be going due to high winds. We didn't know how Captain Bryans would handle it so we loaded up our stuff, got on the tender and headed to meet them. When we got there he was waiting for a call from one of his friends who had was about to arrive at the sand bar. If he got the ok from the friend then we would be able to go. Luckily for us the friend gave the thumbs up and off we went. There were about 20 people on our boat and like the guides were very helpful. It was a bit choppy out in the water and the combination of the waves and the size of the stingrays made our 10 year old daughter terrified. But over all it was a great trip and even my 10 year old enjoyed the 2 snorkeling stops after the rays.
We booked throught RCCL and had the first tender. We only had 15-20 people on the ship to the stingrays. I higly recommend a very early RCCL tour. Last year friends of us (honnymoon trip) were almost too late back at the ship when they booked at a local touroperator. The transport back to the pier was broken down (flat tyre) and after that it was stuck in traffic.