Have only been to Oahu and Kauai. About 5 trips to Oahu and 10 to Kauai.
Quite frankly am in love with Kauai. Keep going back, and loving it more each time. The beauty, the laid back attitude, the (relatively) small crowds, if any crowds at all. Lush, green, tropical, "smallness" non-commercialism (relatively speaking for Hawaii).
I do plan on getting to the other islands, but every trip that comes up, we seem to head to Kauai, especially the North Shore.
If you like to hike, then Kauai is definitely your island, from multi-hour strenuous to an hour stroll in the flowers.
Pick up a guidebook (The Ultimate Kauai Guidebook is the best I've found) and see for yourself.
Enjoy.
Exactly this. We went to Kauai for our honeymoon and loved every minute of it. The guidebook was around even back then. We said we would make it back for our 10 year anniversary. 4 kids and more than 10 years later and we still haven't had a chance to make it back
One day if the kids don't leave us broke.