Keli.....What do you want to do on the islands? Are you the adventurous type who will do zip lines or parasail, climb waterfalls, snorkel or scuba?
Or are you more the beach and suntan type?
Or do you prefer to shop, have lunch and then return to the ship? Maybe you want to take in the local party establishments.
This would all factor in as to the best ports to visit.
I absolutely love Carnivals private island Half Moon Cay. This is as close to paradise as you will get. What a great day to just lay on the beach, have a few drinks and enjoy the beautiful water. I also love Grand Turks. Another lay on the beach and/or party at Margaritaville right off the ship. Cozumel is one of my favorite ports for excursions and for partying at Senor Frogs or Carlos and Charlies. So much to do here! Grand Cayman is a great stop. If you go you must swim with the stingrays.
We did the Carnival Conquest in Feb 2005 and went to Montego Bay Jamaica, Grand Cayman and Cozumel and had absolutely perfect weather.