Maui is rural and full of natural beauty but with some upscale tourist hotels as well. We stayed down in Wailea which has nice resorts, restaurants, and beaches. We also drove all over. The famous Road to Hana made much better with this audio guide, although I regret not planning more time to stop and go swimming in the waterfall pools. Also Lāhainā which is interesting for its 19th century history. The helicopter tour of Molokaʻi was also phenomenal.
Oʻahu is much more urban. The North Shore has some nature but we never left Honolulu. Waikiki is remarkably convenient for a simple carless visit, I totally understand why people go just there for short vacations, but then Hawaiʻi has so much more to offer than one tourist mall! One highlight of Oʻahu was the Heart of the USS Missouri tour at Pearl Harbor, crawling around the engineering rooms of a 1940s battleship. The other was the Bishop Museum’s phenomenal collection of Hawaiian cultural artifacts, made more special by visiting with a friend who is an anthropology professor. We’re not really relax-on-the-beach tourists so it was nice to have some more organized activities in Honolulu.
We are food tourists though! Got some great advice from folks. On Maui my favorite meals were at Monkeypod and Mama’s Fish House. Spago was also very good although not particularly Hawaiian. On Oʻahu the most interesting local meals we had were at The Pig and the Lady and Mud Hen Water. We also really enjoyed Hy’s for wood-fired steaks and La Mer offers an excellent fine French dining meal.