I look at the ingredient list and personally I only choose those that has one and only ingredient: 'milk', because that means 100% pure milk. I avoid those ingredient list with milk solids, stabilizer, emulsifier, etc, coz it's not 100% pure milk and imo i don't want artificially added vitamins and minerals in the milk too.
What I do is I compare the nutrition content of a few brands and pick the milk. I didn’t drink just one brand. I rotate a few Brands. Just look out for pasteurize or UHT in the label. Cholesterol or Low fat depends on what u need.