I've tried sushi at CG and at Kona Cafe...I thought the sushi at CG was very good, I had the deluxe sushi platter for dinner. The sushi was fresh and prepared well.
My experience at Kona was awful and I will not be going back. First, we had a ressie and still had an hour long wait. When we were finally seated, the quality of the food was poor. DD10 and I shared the sushi platter for two and it was just, well, bad. There was way too much rice on the maki rolls and the fish was warm. After a few pieces, I just had to give up. I eat sushi all the time and this was just too fishy tasting--good sushi should have a sweet and clean taste. DD10 ended up having soup from the kids menu (one nice thing, the CM didn't charge us for DD10's kid's meal, since she only had soup). DD13 had the noodles and she liked them. DH had the NY Strip which was just ok. Dessert was the only highlight of the meal and it was delicious...I had the chocolate fondue, DD13 had the Kona Kone which looked fabulous. So, next time I stay at the Poly, I might drop by Kona Cafe for dessert, but I'd plan on eating sushi at CG.
Hope this helps!