If you want to go around Oahu and you are really short of time, then you have to rent a car. We rent a compact and it turned to be a Ford Focus. Remember that Hawaii is United States, so compacts are not like in Europe.
On a whole day you can drive all around Oahu and visit the major beaches of the North Shore.
You do not necessarily need to rent a car on Oahu, at least for the majority of your visit. The Waikiki area is easily accessible on foot, and most island attractions, including the USS Arizona Memorial and the Polynesian Cultural Center can be reached via public bus or a hotel shuttle.
I do recommend renting a car for at least one day of your stay so that you can drive up to the North Shore of Oahu. You really must see this area while you're on the island and the best way to do it is by car. Then, you'll have the freedom to stop when and where you want to and set your own pace.
Rental cars are readily available at the airport. There is also a Hertz rental car desk at the Hilton Hawaiian Village.
THE CONGESTED TRAFFIC WILL BE IN THE OPPOSITE DIRECTION IN THE EARLY MORNING.. SO YOU ARE OK..MOST OF THE TRAFFIC WILL BE COMING INTO HONOLULU ( TO GO WORK )..BUT YOU WILL BE HEADED AWAY FROM HONOLULU ..SO IT SHOULD ONLY TAKE YOU THAT 44 OR MORE MINUTES TO THE EWA SIDE...
If you'd like to head up to North Shore for a day of surfing and what not, be aware that you will probably need to rent a car for the day. If you decide to take the transit system, the ride can take 3-4 hours what with all the stopping to pick up and drop off passengers. If you don't want to rent a car, see if your hotel has some type of non-stop shuttle that goes straight ot North Shore.
I am adventurous. But I will say that driving in Oahu was more trouble than driving in China, Thailand, New York, Paris, Rome. Not that it is scary in the sense that people drive fast and out of control, or that it is the opposite side of the road if you are from North America. It is because people are not conscious when they drive.
The street signs change randomly, and they will close off the highways randomly if a leaf falls the wrong way, and it will take you all night to find your way back to your destination. If you are staying in Waikiki or Honolulu there is no parking WHATSOEVER.
If you are in town to go surfing on the North shore in the winter or to travel around the island as a family, meet people or take a tour bus.
When you ask directions, people will give Hawaiian directions. If you want to know what this means ask me and I will try to explain it.
Honestly, I came to the Island to visit friends and family. I got lost. Multiple times. And downtown parking is expensive and almost impossible.
Take a tour or hire a guide or find people to drive you around. In the long run it will save you time and money.
The beauty of an island never lies just in what is a walk from your hotel.
Also the great part about a small island, like O'ahu, is you can pretty much drive around most of the island in about a day.
My girlfriend and I got up early one morning and drove around half the island and got an absolute eyeful of what the island had to offer: we had a fab lunch at a local fav shrimp shack, saw Laniloa, a pennisula of Hawaiian folklore, watched surfers warm up for a local competiton along the North Shore and watched endangered Green Sea turtles make their way onto the shore to sunbathe at Turtle Bay.
Of course this is only a small sample of what we saw during our car tour.
All in all I think a car is the way to go, but you don't have to take my word for it.
You can just sit there on the beach with your fruit machine drink if you like.
If you want to get out of Honolulu or Wakiki, rent a car. Usually unlimited miles and the price is not that bad. If staying outside of the Cities, you have to have a car. We found getting a minivan the best with children and when hauling stuff to the beach or buying tons of stuff, it was great to have that extra room.
Since we had a hotel in Waikiki, we figured that we would not need a car for the entire time we were in Honolulu (took TheBus or the Waikiki Trolley). But since we also wanted to get out and explore the island, we rented a car for two days.
Your best bet is to reserve over the internet...we did and paid $24.00/day (including all taxes) for a Subaru Forrester (an upgrade over the compact we requested). And we rented from the Enterprise in Waikiki (445 Seaside Avenue/Suite C) rather than from the airport...saved some more money.
Rent a Jeep . . . I was worried about being able to rent a jeep because some of the chain rental agencies said that they were sold out. I did pre-book my jeep before I got to the Island but I did find out that there are many Jeep/car rental places around the hotels that have a wide variety of jeeps/cars available.
Rent a car. The island is easy to navigate and has good roads all around the island. Unless you want to sit on Waikiki the whole time a car is the way to go.