I had a towel animal that was wearing sunglasses and reading the cruise compass. Another time the animal was watching Dora the Explorer on tv. I always love the towel animals that use our sunglasses or hats. I always bring a stuffed animal with me on cruises ever since I was very young and I love when it is incorporated. These little touches always make the cruise extra special!
I believe St. Maarten is the better port to snorkel. I did the Rhino Rider Adventure back in December and we drove 2 person motor boats to a snorkel spot. The water wasn't the clearest, but the overall excursion and experience was great. I know Royal Caribbean has lots of snorkeling excursion options for St. Maarten.
I consider San Juan more of a historical port and usually walk around the streets.
I always bring my own snorkel (full face mask on Amazon) with me. Labadee had some cloudy water, but I didn't go to a specific area to snorkel. However, you wouldn't have to worry about it taking up your whole day or a large chunk of it as opposed to an excursion on a different island.