You're probably going to Ambergris Caye because you want an out-of-the way, cozy, up-and-coming, cool location to relax.
If that is what you are looking for, then you should stay at Daydreamin' B&B. Rob & Mar are the owners and they genuinely worry about giving you an incredibly hospitable and enjoyable experience. Mar provides a great breakfast each morning, at the time of your choosing, with wonderful baked goods. She and Rob are great hosts and are a wealth of knowledge about the "island." Their staff-members Maggie, Sylvia and Albert are native treasures who elevate the experience. Gracie, Tony, and Molly were canine hosts who nuzzle up to you. They are super sweet.
The four cabana set-up is well-appointed, modern, and extremely comfortable. The bed is easy to sleep in and there is plenty of room in each cabana. Each cabana has a porch overlooking the nearby plunge pool. Our neighbors changed throughout our seven night stay, but all were great people and we were able to have lots of fun conversation. My fiancée and I went out to dinner several times with them.
Daydreamin' is in a prime location, about 1.5 miles north of the bridge leading to San Pedro. It is a short walk to many prime locations, like the Truck Stop, Stella's Restaurant, & Rain Restaurant. Marbucks is part of Daydreamin' so you can always get a great coffee drink!
The price is right too. Excellent Wifi and AC.
Negative: If you want a location on the beach, this is not going to fit the bill. The location is just off the beach, but you can walk there in about 100 steps.
I highly suggest this B&B for a great all-around experience.