Overall, milk is likely the healthiest drink for the cost. There are issues with Allergies, however, and care should be taken to not drink too much.
Milk and water
Water,skim milk and natural juice.
Water and milk (provided they are not lactose intolerant) are the healthiest drinks for children and adults.
It is not a question of which is healthiest or least healthiest but a question of which one is right for you. Children and pregnant or lactating mothers need whole milk. Most people should drink 2% unless there are concerns about excessive calore consumption. These people should drink low fat or even better Soy Milk. Soy Milk is also recommended for those with glutton or vitamin D issues.
The healthiest source of milk for a baby is the baby's mother.
The healthiest things to eat are fruits and vegetables. The healthiest thing to drink is water.
usually low fat milk but it depends on who is consuming the milk