Our trip to Caye Caulker was fantastic. The Seahorse Cabana was very nice and had everything that we needed for our trip. Michael was amazingly accommodating and check-in could not have gone easier (also, he's an impossibly cool person). You will definitely need/want to rent some bikes as the cabana is a bit removed from town. The only potential negative is that it is a bit secluded on the end of the island (and by the airport), but even that isn't really a negative, as being on that end of the island meant that we went by Il Baretto every night on our way to town, which had some really nice live music. The cabana is not on the water, but you have access to the private dock. The private pool area is very nice - there are only 3 cabanas in the area that have access to it so I can't imagine it's ever very crowded. We only saw someone else there once.
If you are looking for a relaxing get-away this is a great place for that. I would very much recommend Caye Caulker in general over San Pedro on that front.