We have been to other islands (Big Island, Maui and Kauai - my all time favorite) so we wanted to try something new this time and went with a recommendation from friends. We booked the same apartment they had stayed in on a recent trip in the beautiful town of Kailua on the windward coast of O'ahu. There were two really nice beaches close by (in walking distance actually if we weren't traveling with kids and a gazillion things) - Kailua Beach and Lanikai Beach - as well as shops (a Whole Foods!), restaurants, etc. We really liked the location, the apartment and the yard it had!
O'ahu is the busiest of all islands, at least around the city of Honolulu. You'll find 4-lane highways, traffic jams, high-end shopping, etc... but only a few minutes away from the city you'll find the typical Hawaiian peaceful little villages, lush landscape and of course beautiful beaches. I loved the mix! We did some sightseeing in Honolulu, checked out Waikiki, drove around the island (well not all the way around, but up to the North Shore and down to the South) went to the beach, shopped in Kailua and explored the Dole plantation. A great mix for us, since we don't like to "just go to the beach". We had planned to do some hiking as well, but it was hot and our beloved 3-year old lady is a pretty lazy walker these days, so we skipped it.
We had a great time, but we also noticed that travling with two little one's who are mobile (Ella started walking a few days before we flew to O'ahu), makes it harder and we could not really relax as much as we wanted (and explore) because they kept us so busy. I would still do it again. Aloha!