Having dived two of the three, I found Belixe the best! At Cayman....because the wind seems to be constantly causing rough seas. I have dive the same sites 3 times on 3 separate occasions off the cruise ship.
Have never dived in Cozumel but been there several times. Many ships and many people!
Belize City diving off cruise ship is great, as reefs protect from strong and rough seas. Water is exceptionally clear. Boat came to ship for pickup and returned us.