The weather in Hawaii is nice at any time of the year. Our winter is their rainy season, but whether or not it rains in one particular area depends which side of the island you are on. The area where Aulani is being built should be nice weather year round.
You will find the lowest airfares in the fall - September through November.
I used to fly frequently through Honolulu when I lived in MN. I haven't been back since I moved back to T.O. *Sigh* I always used Delta, and liked them very much. I like their Airbus 330's. Spacious, bright, with seat back entertainment systems. They fly from ATL and MSP using those planes. They used to have direct flights from DTW using those as well, but the last time I looked, I couldn't find them.
United has direct fights from O'Hare that have good times. Whichever airline you use, look for the shortest flight times. You can get to HNL in a little over 10 hours. Some airlines take almost 20 hours. Yucch.