A cruise allows you to visit a number of islands and you get a day to get a nice overview so that you can decide which islands to spend more time at on a later date. Oahu definately takes more time as you need to drive around it for a couple days as well as visit the Polyoneasian Village, Pearl Harbor, DiamondHead, Wahakki etc, etc. The Big island takes a few days as well to see the volcanos and Hilo and rances. One of the greatest adventures are the Helo rides. We did one on both Hawaii and Maui and had a fantastic time. We booked both via Tom Barefoot Tours and paid less than the ships tours and some of the folks on the same helo both times were ships tours people! Pay in advance and get an additional discount. There may be other companies that do this as well. You can and should also rent a car on the other islands and drive around. We even did that on Maui as we needed the car to get to the helo field.