As a Islander, here is my suggestion.
For shopping: Oahu. Ala Moana Shopping Center, and Pearl Kai Shopping Mall, and something peaceful and different, would be the Windward Mall.
To get away from it all: Kauai or Maui. Very peaceful, people there are nicer and more friendlier than us Oahuans.
Honolulu is crowded and noisy, but for the shopping experience, you cannot beat Oahu.
Well, maybe Maui's Kaahumanu Shopping Mall.
For awesome, once in your lifetime experience. The BIG island of Hawaii. The volcano eruption, the tallest dormant volcanos in the world Mouna Loa and Mauna Kea is something to behold! And Maui has Haleakala with its visually dynamic Haleakala Volcano Mountain and its RARE Silver Sword cactus (grows ONLY on Haleakala on this entire world). If you come in the winter, you could experience snow, ice, freezing cold weather, and sunny beach all in ONE day!