Bread may be considered the best food because it's in expensive, easy to make, lasts a long time and is very filling. It's only down side is that it isn't a very good source for protein.
There really is no best food, but there are a lot of healthy foods out there. Fruits, vegetables, oatmeal, lean meats, low-fat yogurt, green tea (technically not a food, but still...), etc., just to...