I have had great luck with Martin Espinal (at Isaira Tours, the owner). He is a great guy, runs a first class operation and speaks perfect English. See http://www.isairatours.com/
For a first timer, I would say the Puerto Plata tour (the fort, the Malecon, Brugal distillery etc) combined with the cable car. Martin is very flexible and can cater your tour to your preferences. Please tell him I referred you.