Although my wife and I did spend absolutely great days in the JW Marriott in Khao Lak, I would not recommend going to Thailand in June at all due to the weather. This falls right into the Monsoon season and you will have a lot of rain.
If you can go there form October to March, the JW in Khao Lak would always be my hotel of choice: Exceptional hotel, great pool, stunning beach and very friendly personal. I will definetly return.
Adding to your post, If you are travailing for more than a week check out the savings of staying for 5 days on a fifth day free. Also it you are staying in hotels for two weeks check on trading points for a package and saving the air miles in your mileage account.