You need a box for "It depends!" I prefer breakfast there, but like the other posted mentioned, its not worth missing the first hour or two that the park is open. We often make a PS for breakfast as late as possible (usually that's 11:20am) on an EMH morning at MK. We enjoy 3 hours at MK with low crowds and then head over to Chef Mickey's for brunch.
Good luck with your choice.
Leslie