BOMA all the way for us.. we love the food and atmosphere.
However, Kona is very good too! If you're staying at the Poly, it would be so convenient. Check out the menus of each and decide which you like better. I love being able to try some of everything so Boma is always better for us! And, as an above poster said, Boma's soups are to die for!
Now Kona has a new sushi bar attached to it (where the coffee bar used to be), and it's VERY good! They have a tempura shrimp with pineapple and something that's wonderful! And their twist on the California roll is very good! My favorite was their spicey tuna one. So if sushi is your thing, then Kona would suit you better.
Either way.. you'll love it I'm sure. Can't do both?