Grand Cayman is a shopper's island. Although there isn't a cruise port that has not been set up with a shopping mall.
But all three of these ports are noted for their excellent beaches and great diving/snorkeling reefs.
Grand Cayman is also known for Stingray City which is a must see attraction.
Belize is known for its Cave tubing and Mayan ruins.
Roatan is mostly a beach place but it does have some other interesting tours.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007