CleveRocks is right is either Martinque or Jamaica.
On my trip in the fall I would say that 90% of the time that I used the busses (which, was always becuse I didn't rent a car) they used the back entrance to the resort (reserved for WDW vehicles) and started in Jamaica and went: Jamaica, Aruba, Barbados, Martinque, Old Port Royale, Trindad North, and finally, Trinidad South. The DTD/waterpark busses in my expereince have always used the front entrace and gone Martinique, Old Port Royale, Trindad North, Trinidad South, Jamaica, Aruba, Barbados. From time to time it was different, but that was the pattern I expereinced the most.
The main rode that CBR is off Bunea Vista Drive, which in my expereince is usually a busier rode so I think for the most part it is easier for the busses to use Victory Way (back entrance) to get in and out of the resort.