I, too, labored over this decision. It really boils down to what you are looking for and how much you want to spend. We didn't spend much time at our hotel, so I didn't really look into upscale places...I prefer to spend my $$ on other things.
We were perfectly happy at Seven Seas. Great staff, beautiful grounds, reasonably priced, but not fancy. If you want nicer accomodations, try Fountain Blue or Banana Beach.
I believe Lan has a pretty exhaustive rating of accomodations on AC on the Belize First link. Do your homework, use the search feature, and email your top prospects for info. Good luck. You will enjoy no matter where you put your feet up.