The difference between brands of milk, or milk type as the potential of each company... it seeks to occupy a larger market at a low price, the milk will be "quality" or perhaps "quantity" of a type of sugerencial price for each sector and / or in the country (location of the dairy company)
In my opinion, first,different brands have different quality based on cows and production process, the more famous the better. Second,They have different nutrition. Some are only for children, some for adults,some for women.
Basically there is not a lot of difference between the brands of milk. Many dairies will just market their milk to different stores under different brand names.