We always plan to have an early dinner at the RFC at AK on the day we arrive. We have had great experiences there with both food and service. After a long car trip, this restaurant is perfect for us because there is a lot of stuff going on around us to keep the girls entertained.
Tried both and from my experience, DD RFC seems less hectic than AK. At AK we felt rushed, while at DD we felt comfortable and could eat at a normal pace. Both are great -- it's just that AK RFC always seems very, very busy.
I think both are great. You can't go wrong with either one. I would select the one that is nearest to where you're going to be. Last summer I ate at Animal Kingdom for lunch, because I was at that park. Later in my trip, for dinner, I ate at Downtown Disney, because I was meeting some friends. Whatever you do make reservations!!!! The DD site was positively jammed and it was fun to walk past all of those people who were waiting for an hour.
I'm planning on using VK vouchers at AK RFC. Somewhere I read that you can use them towards a steak/lobster combo that isn't on the menu. How do you order something not on the menu? Just ask?