Here's some thoughts. I've been on 3 Royal Caribbean cruises and the Windsurf in the past 3 years.
From a dive stand point the windsurf was the best. The windsurf program had: 1. They have 4 dm's on board, give you a equipment drill and checkout in the pool while at sea on the first day 2. Brand new scuba pro equipment as they just recently started the diving program. (we had our own equipment but it may be important to you from a travel standpoint with 4 divers and the fact that you kept the use of the same rentals stored in their water sports area at the stern) 3. The dive boat came right to the ship to pick us up with our gear, or we were taken by tender directly to the dive operation. 4. We went diving in Honduras, Utilla, Roatan, Mexico, The ship left out of Cozumel so we went a few days early and dove in Coz. The ship is smaller with less activities but the service was excellant, food was great, and you went to islands not normally set up for cruise ships. They also had shore excursions at all stops as only 10-20% of the guests were divers.
The Royal Carribean trips were very nice ships, much larger, with more activities, but I had to set up the diving on my own in some/all cases as they wouldn't guaranty a dive spot on days they had dives set up and I wouldn't go without knowing I would dive. Then I had the problem of getting off ship in time to get to the dive shop which was not possible at all locations due to arrival time.
There's also a R.C. cruise out of Jersey going to Bermuda we did. When the ship changed ports we got off the ship at 6am, took a bus to the next port and was diving before our ship had docked and the dive operator then picked us up and dropped us off right at our ship each day. The island was great with very friendly people and a bus system to get you all over the island very easily.
Hope this helps.