Hey RobertE... I make no claims to being an expert on Belize diving, but I have stayed a week at Turneffe Island Lodge, done the Wave Dancer liveaboard, and done local diving and several day trips from from AC over two trips there, and in my opinion, from a strictly dive point of view, the best way to dive Belize is from a liveaboard... IMHO there is to much to miss if you only do land based diving. The ideal Belize trip to me would be a week on a liveaboard, 3/4 days at a jungle lodge, 4/5 days on AC followed by 4/5 days at Placentia (which I hope to visit on my next trip and see whale sharks!) I love AC and all there is to do there, but if you go to Belize to dive and dive only, then a liveaboard is the way to go.
Just my 2 cents...
Scott