don't book anything in advance right now with the hurricane situation.
Nassau got hit pretty hard and you might divert to another port. Keep your options open, I am not familiar with the particular tours, sorry.
We did the Catamaran snorkel in Key West - the only problem was they took us to a reef to snorkel that was pretty dead so there were not a lot of fish to see.
They have a Conch Train ride you can take around the area that shows you the Key West highlights., But we had the best time just walking from bar to bar - many of the bars have all day entertainment going on and it is a lot of fun.