Tom Philpott looks at the differences in milk from grass-fed and silage-fed cows, http://www.grist.org/article/food-2011-01-19-uk-study-organic-milk-has-healthier-fat-profile.
I’d venture to go beyond the nutritionism of comparing esoteric food fractions and consider the whole product and its origins. Humane treatment of cows, letting them live outdoors and eat fresh grass, goes into the value of the product for me. I’d like a taste comparison, too. I’d like to try it myself!