I'd say it depends on the nature of the adults. (This assumes the menus both appeal to you and you're just wondering about atmosphere.) If you're an extrovert and you love people and noise and kids running around then Ohana is the way to go. If you'd rather be slightly removed and don't want to share your dining enjoyment with anybody you didn't bring with you to the restaurant, then Kona (with a request for a table away from the railing, since it's open to the lobby and the people waiting for Ohana) is my suggestion.
Which ever you chose though, I'm sure you'll have a great time.
I like Kona for adults. It is a quaint little place with some different foods on the menu. O'hana is definately family oriented. The food is more mainstream.
Definitely Kona! The atmosphere is more relaxed than 'Ohana, but since the restaurant is completely open to the Polynesian's lobby, you still feel that you are in the resort.
I would say Kona for 2 adults although we like to eat at both. My kids would run away from home if we skipped 'Ohana and missed the Banana Bread pudding. Come to think of it, I would too.