You sound a bit like me with "something a wee bit less 'city'".
Lots of folks love, love the busy vibe of Waikiki/Honolulu. Speaking for myself, that is not what I want to go to Hawaii for. Before I go further, Oahu offers many things the neighbor islands do not in the way of history. The only palace on U.S. soil is Iolani Palace in Honolulu. Of course, Pearl Harbor, an experience for which I have no words. Beyond moving. There's the Bishop Museum with its fabulous exhibits about the history of Hawaii. All that said, Honolulu is a BIG city and Oahu has just over a million residents. It has skyscrapers and crazy traffic at rush hour. But if offers much. The north and east shores are beautiful. Remind me quite a bit of Kauai.
For us, we love Maui. I love the Big Island of Hawaii (where Volcanoes Nat'l Park is) and Kauai. And there are things I love about Oahu. But for us, it's Maui. Particularly if it's winter and whale season!
Maui is growing, much to my chagrin, but offers a great many different experiences. Kauai is more rural and has the ethereal beauty of the Napali Coast, Princeville and Hanalei Bay. Truly lovely beyond words. Kauai also has Waimea Canyon, called the grand canyon of the Pacific. The Big Island/Hawaii has volcanoes, the most active on the planet, rainforests amazing diversity of climates and geography. The BI has the tallest mountains on the planet, higher than the Himalayas because the Hawaiian mtns. start from the sea floor! So the BI and Maui's summits make for some of the best star gazing in the world.
It would be hard to go wrong with picking any of the Hawaiian islands, but it depends on what you and yours think of when you think, "Hawaii". We go every year, and I truly and deeply love Hawaii, its' culture, its peoples and it's music, etc. I personally do not recommend more than 2 islands tops in your time frame. Travel time, even inter-island, is time consuming and will eat up much of one of your precious days. I think doing a 2 island split would work if that's what you prefer. One thing I always tell people is NOT to over schedule for a Hawaii trip (much harder to do that from a Hawaii cruise), because part of what makes Hawaii special IMO and that of many others, is to just......BE. Be still. Feel the softness of the breezes, smell the sweetness of the air. See colors you don't see anywhere else. Just soak. It. In. I promise a day or 2 of just being still on a beach or on a mountain side will give you great ROI!