Please remember, the first two weeks are The Cast Member Holiday, and although they can dine almost anytime during the coming year, most take advantage during these two weeks. The parks will be lighter than normal, the restaurants will be very busy!
Make PS for those restaurant that your do NOT want to miss.
I agree with everything that's been said. Although we tend to visit during quieter times, and have never had a problem getting seated as walk-ups, we tend to make PSs for any we'd be disappointed to miss out on.