We hardly ever take tours in Hawaii. At some ports we just wander around town (Lahaina and Kona are good for this) while at others we take "The Bus" (Honolulu), and in others we rent cars, which gives you the most flexibility (Kauai, Kona, Lahaina, Hilo). Nearly all of the car rental companies provide shuttle buses that pick you up at the pier. We have had good success with Alamo. Book on-line, then confirm shuttle arrangments by phone with the specific local office.