Funny I was thinking this because so was the Today Show this morning. Check out this story by the Today Show's Registered Dietitian and Nutritionist, Joy Bauer....she does a great job of summing up the truth behind all the different kinds of milk and tells you clearly which could be best for what your looking for (protein versus vitamin D/Calcium rich.
Quick Facts from your Smart Snacker:-Cow's milk will carry the most protein (8 grams per 8 fl oz) and clearly more naturally occurring calcium and vitamin D.
-Soy milk is a plant-based milk so it won't have as much calcium and vitamin D but comes close in protein ( 6 grams per 8 fl oz) and because it is plant-based it naturally has less saturated fat
(I like to drink light soy milk)
-Nut derived (almond and hazelnut) and rice milk are considerably lower in protein (That's why I tend to shy away from it; Although I have tasted almond milk and it is quite tasty)!
-Lactaid, Soy, Nut derived and rice milk are all great alternative for lactose-intolerant consumers