Most tours go to the same locations. You'll enjoy it more if you talk to a few of the guides and go with the personality that suits you.
There are many excellent guides and tours offered here, even inland Maya site tours by Rico of Anwar Tours.
Some guides worth meeting...
Harry Wood of Driftwood Tours aka Caye Caulker Tour and Travel,
Ras Creek of Ras Creek Eco- Tours,
Chocolates Tour- Manatee Tour is the best! Chocolate has worked hard since 1986 to have Swallow Caye designated as a Manatee Sanctuary which came to fruition this year, no one cares like he does.
Rico of Anwars- Altun Ha and Lamanai Tours
The Three Carlos at Carlos Tours.