To compare one to the other, I prefer Saona, but it depends on where you end up. I did one trip as a tour operator excursion and we stopped at the busy beach with all the rest. It was gorgeous and made me want to return but I did it differently then, booking a smaller tour (max 15 people), with a stop at the tiny Catalinita Island tucked into the Canal de Catuana for snorkeling before a picnic on Canton de la Playa on the south side of Saona. The next time I went back it was without the Catalinita stop but we had longer at Mano Juan and that's where the food was prepared and served (mini lobsters, fish and pork freshly grilled on the spot!).
I have pictures of the first trip at:
Saona Island, Dominican Republic pictures from beaches photos on webshots
The second with the snorkeling stop at CatalinITa:
Snorkeling at Catalinita, Saona and Piscina Natural, Dominican Republic pictures from caribbean photos on webshots
The third, including snorkeling pictures from the reef at Canton de la Playa:
Saona Island with Seavis Bayahibe pictures, photos, and videos, from caribbean on webshots
I was disappointed with the snorkeling on the Catalinita tour since we stopped at the Wall and it wasn't the best for a surface snorkeler like I am. The beach was beautiful and there is some shopping (nothing most of us haven't seen before but it's a well-organized area), but there are two areas that tours stop at Catalina too, so you may end up at the other spot. As a half-day tour, the "snacks" offered were potato chips. Pictures at:
Catalina Island, off La Romana, Dominican Republic pictures from caribbean photos on webshots
Pick a great guide to take you there and you'll be sure to have a memorable day at either location. I recommend Seavis Bayahibe.
Island Excursions & Submarine Adventure in Bayahibe & Bayahibe Dominicus
Kaki