With a question like this you will probly get a 50 / 50 split on which is better.
Some people swear by O'hana, others by Kona.
Personally I would go with Kona. It's one of the few Disney restaurants I do not mind paying out of pocket for.
The quality of the food at O'hanas is not as good as it once was – (IMO and to be fair I feel this way about 80% of the TS locations in Disney).
The last time I was there they had switched to the peel and eat shrimp – I also recall they were not great quality.
I also recall the meat being very dry and way overcooked. It’s hard to ruin meat cooked over a fire IMO.
Although it is all you can eat family style if you get a bad waiter or they are busy and trying to rush you out you may not get all you want.
I know I have done these type of meals in large groups and it always seemed that by the time the item I wanted got to me there was none left.
The show itself was a lot of fun as I recall and with a large group I would assume it would be even better.
Also with O’hana I have heard that "The Shrimp and Scalloped Potatoes seem to come on and off the menu, so don't count on either."
I have never been there when they did not have shrimp.
I have always had good meals at Kona, but do hear random complaints.
One advantage for a group as large as yours is there is a bit more of a selection of foods IMO, people can pick what they want and do not have to eat the items on the buffet.
I really like the Tuna Oscar at Kona and that is not something you would not get at O'hana.
I would take a look at the two menus and decided that way. With 11 people it may be hard to satisfy everyone, especially the kids.
One advantage to Ohana (IF you are on the
DDP) is you get starters, salads, desserts and you main meal for 1 TS credit. At Kona you just get your meal and dessert for 1 TS. (and of course the beverage)