Southwest is definitely a great option for Hawaii, as it allows two free bags per person, which is great if you’ll be doing Airbnb and shore diving, as you can bring all your own gear (including lead weights) and also non-perishable food. Plus it allows you to rebook your flights with no penalty. Their rates vary dramatically from day to day so if you are flexible on dates, be sure to check their flexible date calendar. I got my tickets for 40K miles from BWI to Kona, with a 3 hour layover in LAX. One other tip for flying Southwest is that when booking with miles, you can check back often to see if the mileage levels have gone down since you booked the tickets, and rebook them — Southwest redeposits the miles in your account.