In Ocho Rios you want to book with Peat Taylor. It is the most amazing tour and the best and safest. You get the falls plus an island tour with all kinds of places for the same price the ship charges for just the falls. He will also take you back to the ship so you can have a free lunch then continue to tour you. I booked this for hubby and self and mentioned it on the cruisecritic board. It ended up that we totaled 18 plus 3 people who also booked with Peat. I can not speak highly enough about this tour.
In GC we did the stingray tour with Soto cruises and really enjoyed ourselves. The mix up the 3 stops so that you are not in the same spot as the million other cruise passengers that booked with the cruise line. The teach you how to play with the stingrays and held one so my daughter could kiss it (yuck).