We stayed at Turneffe Flats Lodge last year (May, I think) for a week, and dove three tanks a day, and were never disappointed. The resort caters to fishermen, primarily, but does have an on-site dive op, and we were the only two divers (wife and I), so we had a dedicated boat and divemaster all to ourselves. In addition to a day trip to the Blue Hole and surrounding area, we dove a lot on the north end of the caye, including both the east and west sides, and it was amazing diving.
I've been diving on CZM since the mid-80's, and while it is also good diving, I think it has deteriorated somewhat over the years, due to both weather and on-island development.
Given a choice, I'd go back to Belize in a heartbeat.