We spent only a few weeks in Ambergris Caye and Caye Caulker. I liked Caulker much better. Fewer people, fewer vehicles, less pollution (San Pedro was thick with exhaust).
The islands are hot spots, so there is a ton of information out there about them. That said, here are two blog entries that may help you.
(Note, we were on Caulker February of 2016. Hopefully that great little hotel is still the same, as well as the make-shift restaurant…)