That's a tough comparison - S/D grotto pool is wonderful but is different from SAB. SAB is larger - it meanders through a great deal of the property and it has the terrific slide and sand bottom. However, I have seen SAB get extremely crowded and very noisy! It serves 3 resorts - BC/YC/BCV. The Grotto pool never seems to be overly crowded and finding a chair is not too bad.
It all depends on what you are looking for. I really can't choose one over the other.