When it comes to buying milk for my husband and myself, I just buy the cheapest 2%. Usually Kroger brand and if half gallons are on sale, I will buy 2 of those rather than buying a one gallon jug if it comes out to be cheaper.
For my daughter, I buy organic whole milk with Vitamin D added. She is 2 years old and I want to reduce her exposure to the hormones farmers pump into their cows. I believe said hormones are attributing to girls "developing" more quickly and feel any reduction of exposure to this is beneficial.
I would buy organic everything if I could, but, alas, cannot afford it.