I've said before that Capitan Marvin's Stingray city and snorkle 3 stop is the best trip in grand cayman.
Dunns river is a must in Ocho Rios
The Waverunners are cool in Labadee
Cozumel, I really don't have a favorite yet, I think that nexgt time I'm going to take the trip to Tuluum
Post what type of excursion you'd like to take (ie water related, adventurous, shopping, relaxing, etc.....we might be able to help you better.)