Another vote for Chase Sapphire Preferred and 40K bonus.

Gives you both the United option and the Alaska via British Airways mentioned.

Though before you think about airfare via points, might be wise to consider where you're staying for hotels. Points tend to go further for hotels in Hawaii than flights (since except the Alaska via BA rate, air mile levels are inflated to Hawaii such that it's tough to get more than 2 cents per mile in value) as noted here:

http://milecards.com/2714/vacations-...your-best-bet/