tgif, you'll have no problem getting great recommendations from the folks on this site. Part of the answer to your question will be based on how long you plan to stay (hint if your trip is for 2 weeks, you're already trying to do too much).
Here's my quick take. I visited the same 3 islands on a 2 week trip (I guess it's been about 10 years now). Kaua'i was my favorite because the pace is much slower. Don't worry about doing it all, just have fun. I spent more time at the beaches on Kaua'i than anywhere else and I'm glad I saved it for the last part of the trip.
On the Big Island, visit Hawai'i Volcanoes National Park and Pu'uhonua o Honaunau. I took a circle of the island and enjoyed the Kona side better than the Hilo side. I opted to stay at the Volcano House (the lodge in Volcanoes N.P.) Worth considering for one night.
The only Marriott where I have stayed is the Waikiki Beach Marriott. Great place, but others can provide more insight. kharada46 will do a much better job with O'ahu than I ever could, so I'll leave that to him. Most of my favorite places are ones he has mentioned in other posts.
There's lots of history, great natural areas, wonderful places to eat, boating, surfing, biking, helicopter rides, you name it. Let everyone know a little about what interests you and we can help suggesting things you will like.
No matter what, you'll have a great trip.
What type of information are you looking for? I'll do my best to assist you in any way possible! I live on Oahu, so hopefully I'll be able to help you best with that. I've also been to all the islands you've mentioned, so I'll do my best with those!
For starters, let's go over the Marriott properties on Oahu:
Marriott Waikiki v.s. Courtyard Waikiki - this write up is a little date, so I do know that the Courtyard Waikiki has changed their ac unites to split systems rather than window mount, so the ac should be a lot quieter now.
Waikiki Beach Marriott (photo album)
Courtyard Waikiki Beach (photo album)
JW Marriott Ihilani - Post Renovation Wedding Weekend Stay (updated, stay was 08/2013)
JW Marriott Ihilani, Ko'olina Resort (stay 12/2011)
For a good deal on car rentals on all islands, check out this site Discount Hawaii Car Rental Maui Car Rentals Honolulu Kona Kauai Hilo Waikiki.
You don't have to pre-pay your rental and they're very responsive. They saved me a ton vs when I was getting quotes on my own. Your results, of course, will vary and I do have the Kama'aina discount up my sleeve as well.
For inter-island travel, I'd recommend flying exclusively on Hawaiian Airlines as they are the only airlines that offers jet service between the islands. The others will be on tiny single or larger twin propellor aircraft.
For the Big Island, keep in mind, Hilo has VERY limited hotel options. The big brands don't exist there, and the ones that are there are, well, not what you're used to if you frequently stay in Marriotts. My recommendation for a visit to Volcano National Park if it's on your itinerary, would be to stay at the newly re-opened Hawaii Volcano House
But, like I said, let me know what kind of info you're looking for and I'll be happy to assist! In the meantime, please check out my Marriott Rewards Insiders Blog for dining and activities reviews. The newer reviews are mainly Europe, but scroll back and you'll see the Hawaii ones: kharada46's Blog
This may also be helpful
I plan on checking out some of these later this year when I head to Maui