I think it depends on which Caribbean islands you're comparing the beach to. I haven't been to the islands that are considered to have the best beaches, mostly because they're also relatively flat and arid. I much prefer the islands with more greenery, usually volcanic in origin.
I spent most of my time within a mile or so of town and haven't seen any topless sunbathing. I'm sure the further north or south you go, the easier it would be to get away from people.
There aren't any waves to speak of on Ambergris. The waves break on the reef. So, there's sea grass. A turn off for some.