Boma Boma Boma!!!
I've never eaten there, but the rave reviews and descriptions of the food just make my mouth water. I want to try it more than any other restaurant on WDW property, so go for that!
Kona Cafe is really good, but it's also a little cheaper than some of those other places. So while you have the coupon, I'd say try one of the slightly spendier ones!