For Nassau, I have to recommend the Dolphin Encounter. That was awesome and so much fun. DH and I did it back on our cruise in January and were really glad!
If we ever go back, I think we're going to try the Discover Atlantis.
As for CC, when we went the water was a little rough, so they cancelled the Glass Bottom Boat that the Dh wanted to do. When we go back there, I think we just want to enjoy the beach!