I booked through Carnival when we were there in January. booked a two tank morning dive. The dive company only does the cruise ships. They were waiting at the ship when you came down the gang way and you walked directly to their boat. I was pleased with them. They have a nice boat also. The price was almost the same also, I believe $99.00 for a two tank dive and that included gear. The other dive operators the timing was going to be close to be able to get to where they were going to pick you.
The only problem, we did not get to do the two dives and the only dive we did was in the harbor. The seas where so rough that they cancelled the shows on the ship as they could not stand up on stage. It was our first and probably our last. I worked on ships before I retired so I am use to the rough riding, but my wife and others were not. They refunded our second dive and credited it to our account on the ship. Even in the harbor it was interesting getting back on the dive boat, but not bad.
Have fun.