I used Roberts Hawaii for my shuttle to my hotel. I found them to be friendly, reasonably priced and professional. They will meet you at the end of the gangway for domestic flights and just outside of luggage claim for international arrivals. They greeted me with a big smile and a small shell lei.
Note that the closer you stay to Waikiki, the longer you will wait to be dropped off. I was last. Don't be surprised with how long it will take to traverse the 9 -10 miles from the airport to Waikiki. It took over 1 1/2 hr for me. I thought I'd have time for a swim before it cooled down and instead, I ended up trolling the streets for a suitable restaurant for dinner instead.
There are no shortage of Sushi restaurants in Honolulu. I can't believe there is enough business to support them all. I ended up eating at an Asian seafood restaurant frequented by movie stars and Presidents of the US, past and present. The food was good, not mind blowing.
Waikiki beach was different from what I had pictured in my mind. In fact, all the beaches I saw on this trip were. It could be I wasn't in the correct place, but the beaches weren't the long expansive ones. The sand is coarser than you would find in the Caribbean and the colour of the water is definitely Pacific Ocean -- Darker, with occasional turquoise.
In the case of Waikiki, the erosion was severe enough there was a good 3 - 4 ft drop to get to the water. Active effort was underway to truck in sand from drudging a nearby river so expect areas to be fenced off. The beach I visited in Lahaina Maui, had a pretty fierce (for me) undertow not far in from the water line.
I flew with Blue Hawaiian Helicopters in Kauai. Would definitely fly with them again. Regretted not signing up for another flight on time when I was on the Big Island. I would return to Hawaii just for the helicopter tours.
On their website, there are a few minutes of video intros of each island worth watching. Looks like they offer discounts for booking online. I wasn't aware of that as it was a spur of the moment thing for me.
There is a pub located in the same small plaza as the Blue Hawaiian office in Lihue called The Feral Pig. The staff there are really friendly and the menu is diverse.