Sosua and Cabarete beaches have different "vibes". Sosua is calmer and better for swimming and snorkeling. Caberete of course is a windsurfers mecca and a younger crowd. Food and drinks are a bit cheaper in Sosua.
For a change of pace and a really gorgeous beach with a less "touresty" feel. head East about 45 minutes from Cabarete to Playa Grande, near Rio San Juan. The seafood served from the fish shacks on the beach is fresh cought, well prepared, and reasonably priced. While in the area, you could take the boat tour of Laguna Gri Gri in RSJ.