I've been to all the islands, but I like Maui the best.
The absolute BEST breakfast in Maui is the Gazebo restaurant. It is a little hard to find, and is very small, but I still dream about their white chocolate macadamia nut pancakes. They are insanely good! Plus, you are looking at a spectacular view while eating. You are actually in a small gazebo.
The best, most romantic restaurant for dinner is Kimo's. It is outdoors, right on the ocean, with spectacular views and even better food. The tables for two are right on the edge of the deck, and both chairs face the ocean. We always eat there at least twice every visit. Also, I am one who can usually take or leave most fish, but their fresh fish prepared a million different ways is worth the 9 hour flight alone! We used to like the Hula Grill, but the last time we ate there it was horrible, bordering on inedible, and I am not one who is very picky. I'm not sure what happened there...
Also, if you are tired of spending $150 a night or more on dinners, there is an unbelievable burger place in downtown Lahaina. It is called the Fat Cat Grill or something like that. HUGE burgers, and lots of different, unique options. I think they were around $12 a piece which is cheap for Hawaii. Plus, it is on an upstairs deck overlooking the main drag in Lahaina so the people watching is stellar!
One more tip--buy an Entertainment book for Hawaii! Usually they go down to about $10 around March or April with free shipping on their website. There are tons of buy one get one free dinner options, plus lots of coupons for parasailing, tours, etc. It was more than worth the money even if you only used it once or twice.
I HIGHLY recommend getting the Maui Revealed and Hawaii Revealed books. Tons of great information, and it is written by a local so he tells you all the great little places that don't make the other travel books. That's how we found all these spectacular little beaches. We went to a different one every day, even though our hotel was beachfront. Have a great trip!
We've eaten just about everywhere, so if you have any other questions, let me know!