Last year (August 2008), Kona was not as good as it had been in prior years. Our server was off, and the food was decent though not great. It had been much better before; I'm not sure if we caught it on an "off" night, though.
We also had dinner at the Wave, and it was quite good, though we had a very annoying server who confiscated my KTTW card at the beginning of the meal and wouldn't give it back until after we were done dining, but beyond that strange interlude, the food was good.
In terms of atmosphere, Kona is much louder. The Wave, though not really special, is quieter and calmer.
Good luck choosing!