Roatan: we took the ship's excursion to Tabyana Beach, based on recommendations from friends who took the excursion last year. It's a beautiful beach, drink service is very attentive, snorkeling off the beach is better than I expected, and you can walk down the shore to stretch your legs.
Belize: we went with Coral Breeze Tours on a snorkeling tour to Caye Caulker and Shark Ray Alley. Awesome! Fantastic! With the exception of scuba diving on the Great Barrier Reef and in Bermuda, this was the best snorkeling I've ever had. Shark Ray Alley in particular was wild - so many rays. There were a few rough edges in the course of the day, but nothing serious. I highly recommend Coral Breeze if you want a fun snorkeling experience.
Costa Maya: we went on the ship's "Down and Dirty Mini Jeep Adventure". Lame and not worth the money. If you've never been on an ATV you might find this to be unique, but We own ATVs and found the trails and scenary to be boring. Last year we took a tour with The Native Choice Tours, and that was ten times better - if you haven't used them, give them a try.
Cozumel: we've been to Cozumel several times before, so we took the ferry over to Playa del Carmen for the day and had a blast. The shopping is concentrated and excellent, and the beach is beautiful.
Last time we were in Cozumel we took the "Cozumel Bar Hop Tour" from an independent vendor, and it was excellent - highly recommended. If I didn't go to Playa del Carmen, I would have gone on the Bar Hop tour again.