When I was in Belize, I was working as a marine biologist/underwater videographer for a Lindblad eco-cruise ship. We were able to stop almost anywhere along our route to dive. A number of dives were on Lighthouse Reef and Long Caye. After that I spent two weeks on Caye Caulker, but we couldn't get out past the reef due to strong winds. Depending on where you've dived before (I prefer Asia and the South Pacific), I'm sure you'll enjoy your experience in Belize.