I took Southwest to Hawaii last summer to see how it compared with other carriers. Honestly, the flight was fine - if not a bit long - for a typical flight on Southwest. The expanded snack box was nice and the service was top-notch as well. Southwest's fares are extremely competitive, and they are perhaps the most cost-effective of any airline serving Hawaii.
I few from Las Vegas, which made it roughly a six-hour flight.
Compared to my first flight to Honolulu in 1982 on United, the Southwest flight was bare bones. On the United flight there was free headphones, a nice meal, and it was a 747 wide-body plane. Southwest flies to Hawaii like all their other hops with a Boeing 737.
Needless to say, the United flight was like flying to Hawaii as a king. Of course, much has changed in air travel since that flight and it's really an oranges to apples comparison.
My daughter fly to Australia via Honolulu on Hawaiian this winter. On her flight, Hawaiian offered a variety of perks that other carriers do not, like complimentary headphones, a lunch, and free allocated seating. Funny thing though. She said it was a close experience to the Southwest flight, with the exception of the meal. Meaning, she wasn't all that impressed with the service or the airline.
It should be noted Hawaiian has an excellent on-time reputation and is conveniently located at Daniel K. Inouye International Airport in Honolulu. Also, Hawaiian provides the most reliable domestic service between the mainland and Hawaii. After all, it is their home turf.
Hawaiian Airlines also flies the Airbus A-330. It has a wide body and seating in a 2-4-2 layout, which means you are never more than one person away from the aisle. This is vital given you will be on the plane for nearly 6 hours.
Once you arrive in Hawaii, you will most likely travel on Hawaiian between islands, therefore you should consider them when you plan any inter-island stops.
Don't forget your points: Hawaiian Airlines or Delta Airlines offer great mileage programs. Cheap is also good, and right now all of the airlines are offering great prices on roundtrips between the west coast and Hawaii.