Where is the best place to go in the Dominican Republic?

So a friend and I want to do a girl's trip to the Dominican Republic...5 nights most likely. We want to enjoy the beach and have an all inclusive resort and a nice beachfront hotel, yet be able to do small excursions. The most important thing is the beach and relaxation. (We are on a budget so we can't be too extravagant but we want nice accommodations, just not too high end.) What part is the best to visit??