Both are good. We like them both. They are different experiences. PF has characters and being buffet has something for everyone. Kona is s sit down restaurant with good food. With a group of your size you're probably better off at PF. One reason is you are more likely to be seated together (PF has some large round tables). Tables at Kona are smaller and they'll have to put 2 together for your group.
The food at PF is very good. One of the best buffets on property (IMHO).
Have fun!
ADDED-I just read some recent review, comments about PF and I'm disappointed. Seems the quality and choice of foods offered has changed. I'll be changing my ADR there. So, my choice is KONA CAFE!