The Cabanas are the most frequenly requested -- 9B, 8A, 8B and 9A. Then it would be the Castias, Casitas 4 and 5, followed by the rest. The Ranchos are the least requested because they are the furthest from the main building.
We have stayed in Casitas 2, 3 (twice), 4 (2 times), 5 (2 times) and Cabanas 9A (our most recent stay). Personally, we prefer Casitas 4 and 5. This being said, we are requesting Ranchos on our next trip to give that area a try.