I highly recommend the Moca road via Sabaneta... the north shore is known for its bad roads, but that road is delightful. Not a pothole in sight, very little traffic, breathtaking views, and an excellent stop at the top for coffee.
Moca is about 10 minutes from STI Airport. Why go to Puerto Plata to rent a car? Hell you can just about walk to Moca from the airport. Didn't this occur to anyone else?