I stayed at the J. W. Marriott Ihilani in the winter of 2004. What a grrrrrrrrrrreat hotel! Amazing lagoons and good location! It's about twenty minutes from the crowds and tourist traps of Honolulu and Waikiki, so if you like quiet like me, then this is the one! I don't mind giving away my little travel secrets to Hawaii, since I've pretty much done it all.
The best time to book a trip to Oahu is right after New Years. I'd say...give it a few days after New Years because a lot of New Years guests need a couple days to get all sobered up and such... Why is this the best time to go? Because all the holiday travelers hafta get back to the real world after the holidays! Sooo...many hotels are nowhere near their ideal capacity. This also ups your chances of getting a nice upgrade to an ocean view room. No need to book ocean view, really.
Oh yes, this is also the NFL Holiday Bowl's hotel of choice, so this is another great reason why booking AFTER the Season is good. All the hustle and bustle from the NFL crowd has wound down.
Why I like this hotel over others on Oahu are for these reasons: 1. It's far enough from Honolulu so you don't feel the congestion and chinsy touristy things, but close enough for an enjoyable drive into town in that rented convertible. 2. Great beds, great laid back hotel that isn't TOO big and pretentious like the Mandarin Oriental or the Halekulani. 3. The resort has a great golf course. 4. Paradise Cove Luau is a 2 minute drive away. 5. The town of Kapolei is ten minutes away and has all the conveniences of the stores you may find at home.
Happy travels. :)