If you want to fly to Hawaii and just cruise the islands (7 days) then you are limited to only Norweigan Cruise Lines. If you want to cruise to and from the mainland and see the islands (15-17 days) then you have a number of options out of San Diego or LA or San Francisco (occasionally Seattle or Vancouver). We have done it twice on the Island Princess (out of LA) and once on the HAL Statendam (San Diego), and had great trips both times. They all do the same ports in Hawaii.
One thing I liked about the Statendam trip is that while you only get a 1/2 day ashore on Kauai, they use the rest of the day to travel on the ship all the way around the the Napali coast, which is nearly impossible to see except by boat or helicopter. We were there in March, and there were whales leaping and swimming all around the ship and we had spectacular views. HAL also makes a point to make a big deal about seeing the lava flowing into the sea on the south shore of the Big Island. On our last Island Princess trip they did not come close enough to shore to see it, and said there was nothing to see, while friends of ours who did get up at 2AM to check stated there was lava to see. Many were disappointed.
The Island is a newer ship with many ammenities, and is probably better if you have young children. We need a wheelchair accessible cabin for 3, which is hard to get, and there are more of these cabins on the Island than on most HAL ships. The food is better on HAL.
Have not done this trip on Celebrity, but would like to as we have had good experience with them in the past. RCCL is not our favorite.
Hawaii is a good destination for renting cars and doing things on your own. What are your interests?