Definitely snorkel or scuba dive if you are in the keys. Captain Albert and first mate Mike were great. The ride out to the reef is about twenty minutes, not long at all. Once there, the boat anchors in deep water and you swim a bit over to the reef. This is a little scary at first, but our kids, ages 12 and 11, handled it fine. Mike gave quick directions on how to use the equipment. It's pretty easy, though if it's your first time, get used to breathing with your mask on before leaving the ship. Mike told us quickly which direction to swim in to get to the shallow part of the reef and then that was about it. You're on your own, which is fine, but the ship was moving around so as we looked to it to get our bearings on the shallow part of the reef, it got kind of confusing. I wish they would have a pointer or something on the ship to guide you as you're in the water.
All in all, we had a great time and did fine, but if you are first-time snorkelers (we are not), I think a guided tour or one that offers more directions would be worth the added cost. For experienced snorkelers who like to just jump in and go, this tour is great. You get 90 minutes in the water and it goes by fast. We took the 3pm tour on a calm day and had great visibility. We saw lots of coral and beautiful fish and even dolphins, no turtles.