Our main Hawaii trip is to Maui, although we haven't been back since the Lahaina fire. We will likely go back next year. We really enjoy the mix of nice places to stay and eat, with amazing natural wonders, e.g., Haleakala, snorkeling in Hanalua Bay, hiking in the West Maui mountains. Kaui is lovely, too--a little less "touristy," but probably for the reason that its natural wonders are a little more isolated/harder to access (and it's rainier). But it is beautiful. My impression of the Big Island is it is for volcanoes. If you like volcanoes (and who doesn't?), it's the place. I've only been there once. I've been to Oahu a couple of times. It's the Big City version of Hawaii. Still beautiful, still tropical, but Waikiki is a big city. Not my style of tropical vacation, but it is for a lot of people (and of course there is the north shore and the Disney side of the island, which I'm sure are great fun). I did really enjoy visiting Pearl Harbor, and we have a family member buried at the Punch Bowl (the national cemetery), which is a moving and beautiful place.
The flight isn't bad from here: about 4 hours there; five hours back. Quicker than going to New York.
All of which is to say that we're a Maui family (Kaanapali), but there's nothing wrong with the other islands. :-)