I agree with both of these suggestions. If you have been to one and not the other, then do the one you haven't done before. If you haven't been to both, then do some homework about the different ports to see what they have to offer and pick the itinerary that best fits your lifestyle and your interests. Some ports are more for shopping (St. Thomas as one example). Some are best for beaches (Grand Cayman & St. Maartin). Some are wonderful for sightseeing (St. Lucia). Really depends on what you're looking for.
Talk to your agent, they can be invaluable with providing information about the ports. Plus, they'll be able to help you with determining whether the Carnival Breeze is the best ship and offers the best itineraries or whether you might find something else more to your liking.