We're staying at the GF and have ADRs at both of these places in August.
We've had dinner at Kona three times in three years. It's okay, but I think the quality has slipped a bit, and the atmosphere is pretty basic. That said, my kids like it, and it's certainly acceptable to us.
We had dinner last year at the Wave. The food there was a bit better (IMHO) than Kona's last year, but our service was not the best. In terms of atmosphere, the Wave is much quieter than Kona.
I haven't been to the Grand Floridian Cafe, so I can't comment.