Are you paying out of pocket or have a dining plan?
It's a toss up between Brown Derby and Mama Melrose for me. We did deluxe dining last summer and though I loved the atmosphere of Brown Derby..the food was just meh. It was packed, the meal took forever, and nothing stood out as really noteworthy.
Kona Cafe.. I would do a whole meal. It gets really good reviews.
We love Biergarten but I have not seen the soup on my last two trips.
And O'Hana.. my kids loved the breakfast. We aren't huge Stitch fans either but there were quite a few characters and we had a great time. It seems like the perfect way to end the trip
Oh.. and I would resist making too many changes. I think it's the ADR doubt that creeps in just before the trip. You booked them for a reason and you'll enjoy them when you are there!

(At least that's what I keep telling myself lol)