It has been proven as better - for infants. There are nutrients that are produced in breast milk that are necessary for the development of newborns, mostly in their digestive process. It is a bridge to solid foods. Once a child is on solid foods, milk from a cow is not really the next proper step.
Milk has a foothold as a healthy drink because of it's calcium benefits, but many people in the know in the realm of healthy eating downplay the necessity of milk from any source once on solid foods. Of course, the milk, cereal, cake, industries, etc. will continue to push the virtues of milk, but soy milk is the healthier alternative for children.
Point is this: breast milk is better for infants. A good diet sans any milk is good for anyone older.