Originally Posted by PsiFighter37

With that much time (very jealous!), I would definitely split between 2 islands. If you do want a taste of Lost/5-0, I'd staple 2-3 days on in Oahu at the end if you are set on that (as you'll most likely be flying in/out of HNL if you are coming internationally). Aside from that, definitely take a look at what Kauai, Maui, and the Big Island have to offer. I haven't been to Kauai for a long time, so my memory may be rusty, but it is definitely less populated and more remote than the other two. Whereas Maui and the Big Island both have some population centers, Lihue (which is the city you fly into on Kauai) is a pretty sleepy town with not much to do. Gorgeous scenery to see, and lots of outdoorsy stuff to do, but if you're looking to trek into 'town' at all, Kauai isn't the island for that.

If you do consider spending all your time on one island, the Big Island is the place to do it - so many different parts of the island to see, and the farthest you'll ever have to drive in one shot to get somewhere is ~2-2.5 hours.