I ordered a cab ahead of time and saved some $'s. I called as soon as I landed and someone was waiting for me at baggage claim. Pretty good for cab service!
If you are staying at Waikiki, surely you can spend a day or two without needing a car and then just get a car for a day or two to roam around the island. Since you don't want to pay for parking in Waikiki, its great to rent for the day there and return.
Its a quirky garage location and a little far from the hotels but its workable and can save you a lot on the rental charge and hotel parking.