I think I might be the oddball, but I thought diving in Belize was the best. Just returned from Cozumel and the diving was great but preferred Belize. It is probably easier to get from a cruise ship to a dive operation in Cozumel though.
Cruise ship to dive operation in Cozumel is probably 15 minutes. ( I didn’t cruise there, stayed at a resort.)
The boat ride from the mainland in Belize to Ambergris Caye is about 45 minutes (it’s about 15 minutes flying but cost around $100).
-Audrey