I've only been once and used Capt. Marvins, but I was really impressed. It stormed in the morning while we were there, and they drove us around the island waiting for the storm to leave, giving us free trips to Hell and the Turtle Farm (didn't go in the Turtle Farm, but saw it). We had a full day, 2 snorkel, lunch and stingray excursion paid, but they ended up only charging us for the half day. They didn't offer it, but when we asked they did it. I liked our tour guides a lot.
I can't compare them to anyone else, but my husband used them 10 years ago, and they are still just as good.