Wow, that's a hard one. Western or Southern would be my opinion.
Southern out of San Juan will have lots of ports. That is the other thing. Do you want more port days or days at sea - Caribbean sunshine & relazation on board ship. From SJ, you will usually call on St. Martin, St. Thomas, Antigua (356 beaches), Barbados, St. Lucia or Martinique. The last is the least desirable, but the beach at Pont du Buc is nice.
Western out of FL: Cozumel = Paradise Beach Club; Grand Cayman = Seven Mile Beach; Jamaica = either Ochio Rios Dr. Cave Beach, Rose Hall Beach, Negril, Mahogony Beach, etc. and a nice private island like Labadee or Princess Cays= beach day with full barbeque lunch.
Check out the length of time in each port and make your decision from their. Grand Cayman is usually the shortest day.