Hawaii used to be a far-off dream for me. I live in New York so airfare alone can be expensive. However when my then-fiance and I were considering destinations for our honeymoon (September 2016), we realized that Hawaii was actually within our reach, and what better time to do it. I was able to use TrueBlue points (JetBlue) to redeem one round trip flight, so we only had to pay for one ticket.
So off we went to Kauai for about 6 days. We stopped over in Oahu for about 24 hours so we could see Pearl Harbor, but our main destination was the north shore of Kauai. We stayed at the beautiful Hanalei Bay Resort in Princeville.
Kauai is certainly the more "romantic" island, and very lush and green. But it also requires a sense of adventure in order to really appreciate all the island has to offer. This is not the island for just lounging on a beach all day. Some of the highlights of our trip were a helicopter tour of the whole island (seeing the "Jurassic Park waterfall" and Mount Waialeale), a boat tour of the absolutely incredible Napali Coast, an 8 hour hike along that same coastline and up to a secluded waterfall (Hanakapiai Falls), and seeing Waimea Canyon ("the grand canyon of the pacific").
Here's a tip - you definitely need to rent a car to get around the island (side note - you cannot drive a full circle around it, so going from one end to the other and back is a trek) but do yourself a favor and go with a reputable rental company. We tried to do a budget company, Kauai rent a car or something like that - and we got a really old car, squealing breaks, sounded like it was on it's last legs. It got us around but we were uncomfortable driving it. This company's method is to leave the car at the airport with the keys in the gas cap and you just pick it up (after paying up front) and then drop it off in the same location when you're done. Interesting and sort of convenient but not worth getting a rust bucket of a car.