Well, the north shore of Oahu (funky, laid-back) and the St. Regis on Kauai couldn't be more different! (I might equate the north shore of Oahu with the north shore of Kauai everyplace other than Princeville ).

You sound alot like my husband and I in terms of travel. Kauai has some incredible hiking/waterfalls, etc...We took a helicopter ride over the island and it was pretty amazing as you go from desert to "jungle-like" vegetation and it looks like you are in a head of iceberg lettuce or something. Molokai - as you probably know - is the least inhabited so that has some appealing aspects in my book. About 8 yrs or so ago I had found some pretty cool "yurt-like" luxury tents in Molokai - I thought it was at Hotel Molokai, but I can't seem to track them down anymore when i google them so maybe they are gone now.
Lanai - in my opinion, going to one of the 2 major resorts (Lana'i at Manele Bay and Lodge at Koele) seem to be the draw to Lana'i.

We stayed at the SR in NYC recently and FS in Wailea. Laid back but not funky. Maybe we are bipolar travlers.

Gosh, that's a lot of time in transit.

What time of year will you travel? Kauai's most gorgeous north shore is best in summer when oceans are calmer and it's NOT RAINING. (Rather similar to North Shore Oahu.) To the south, Poipu may be too 'touristy' for you -- though nothing like Kailua-Kona. (What a diaster.) You might find something to rent near the canyon. I'm not fond of the hotel at Princeville -- originally built to impress Japanese tourists and still not "Hawaiiana" enough for me. But I prefer a resort condo and 'home away from home' in Hawaii over hotels. (After two to four weeks on all four major islands over the years -- and coming in winter -- we chose South Maui.)

I haven't looked at inter island flights lately but have done the Molokai/Lanai combo. You will likely have to travel from Molokai back to Oahu to then get a plane to Lanai. The options on Molokai are very limited.

While we loved our visit to Molokai - and had a wonderful hike into the waterfalls/pool at the east end, and also drove out to the west end and also up to look down on the Leper Colony - and while I only was on Lanai for a day - looking at some property - and loved it - our favorite remains Kauai - the true Garden Isle - and there is so much to do there.

I think the Saint Regis is amazing, but it's definitely more of a destination resort type place, v. being able to just go outside say a rented house further out/beyond Hanalei - and pretty much have your own beac.

There are other options on North Shore - at Princeville, or in the Hanalei and Anini Beach areas - and trust you have read Sondoc's great reviews.

Years ago my sons and I spent a eeek on Molokai and we all still talk about it. We did not stay in the condo village but rather in the Pau Hana which now I believe is no longer there.

We spent days driving around and just enjoying being part of the life. We did hike up to the water fall and it was just rugged enough to be fun.

After dinner we would get ice cream at the Dairy Queen and then watch the locals play baseball. Within 2 nites we were part of the famllies.

We flew from topside down into the Leper colony and had a miracle of a day tour Henri was our guide and he is still remembered with love. Don't miss the opportunity to tour the colony...it is spiritual and magical.

I think of all the islands, and I have seen the all but Lanai...Molokai is my favorite and it was cause there was really nothing to do and only the locals to spend the time with!

Swanner, you are referring to the Molokai Ranch, which closed in 2008, due to a dispute over further development not being allowed on their site. We actually dropped into the Lodge there, a couple years before closing but did not see their "luxury tentalows", as we were there only on a day trip.
We did stay at Lanai in 2010, for 3 nights, and I'd like to get back to Molokai for 4 or 5 days in future. The slow pace can be somewhat appealing, at times.....
Lanai and Molokai are so unlike the other islands. As with the rest, they are similar, but different! Definitely, both are worth a look.

Thanks everyone. We are beginning to look at a rental in Hanalei, but are not committed to that yet. We probably need to decide something soon, as it appears some rentals are already booked through the first part of next summer.

Good choice in terms of choosing Hanalei in the summer. You are right about rentals booking up quickly. It is a HOT vacation rental market. People often re-book the same house for the same period year in, year out, which can make it harder to find exactly what you're looking for. We like to rent places right on Weke Road. This is the first year that we are staying in a place on the beach. Can't wait!

Here's an old trip report for Molokai and Lanai. However I think for this trip you might be better served to relax and explore on Kauai

http://www.fodors.com/community/united-states/molokai-and-lanai---a-trip-report.cfm