We usually eat breakfast at the resort. We are always too late for breakfast by the time we get to the park.
I do find that the breakfast at the CS in the resorts are sufficient. We usually order the egg/cheese croissant or the breakfast platter and eat it in our villa.
We also utilize the refrigerator in the rooms for milk and other drinks as well as yogurts etc for quick breakfasts. However, we have yet to use the stove to cook anything in the villas. But we have used the microwave to heat any muffins or pastries.
We did make a mistake and tried to eat breakfast at the Main Street Bakery at MK once. It was extremely busy with very limited seating.
A few vacations ago, we had breakfast at Sunshine Seasons at Epcot. Although it was less busy, the food wasn't that great. I preferred the ones at the resort.