To a certain degree it depends on what you like to do and the ship that you intend to sail on. Days at sea can be great days when you can do so many things on the ship at little or no cost with other people or just rest with a book or sunbathe and swim. Port days are also exciting or relaxing but do generally cost more than staying on board. The day before disembarkation is always spoiled and some of it used up because you have to pack and that day is normally a sea day when it could be better spent as a port day but there are few calls other than Key West close enough to the cruise terminals.
So to sum up if you think you are going to enjoy the ship then two sea days might be best but with only seven days it's a tough decision. .... Neil
In practise 1 day in each port is usually sufficient in the Caribbean
You can generally tour a whole island in that time and see pretty much everything although not in the larger islands like Cuba
Having been there 4 times I prefer to visit a lot of ports and particularly if it is your first time I would recommend this
My favourites are Barbados Antigua St johns and Tortola but most of the Islands have lovely beaches and the bluest sea you could imagine
If you dont want to leave the ship on port days dont. If you enjoy sun and swim then port days are the time you can go to the beach or you have the ship to yourself !! no fighting for sunbeds. Swim without being 'bombed' by teenagers and mis behaving adults ! No queues in the restaurant.
Research the islands on the cruises. Most you can do on your own then you wont have to be up at 7-7.30am to go on a shore excursion. You can get up later, enjoy a leisurley breakfast and then go out and see the sights by taxi which are now free of the coachloads of ships trips !! Enjoy lunch out and chill like the natives. That will take 4 hours of your day only. You need not spend anymore than that. Choose a cruise that has the whole day in port to reap the benefit. 1 day at sea to get used to the ship and adjust your time zone is fine. 2 days, you will regret and anyway, you WILL be back as cruising will be in your blood and the islands will draw you back again and again. Enjoy!