I use Knox. I buy grass fed beef, but grass fed gelatin is a waste of money. Gelatin is just made from bone; there are no hormones in the bone like there is in the flesh of the animal. Your body breaks down gelatin to its constitutive amino acids and doesn't care about the source. Glycine from a grass fed cow is the same as glycine from a corn fed cow.
@MaverickRaj Bone is tissue as it connective tissue used to make broth. In simple term all of this is made of one thing, what you eat. An animal fed on its natural diet (cow's eat grass) will be much healthier than those made to eat a diet that is unatrual to them. You only have to look at the decline in human health due to processed foods to see this. So to say that the body does not care about the the source of its food is extremely short sighted. I respect that this may not your choice and you should do what you feel is right for you, but in my clinical experience this is quite the opposite of what I see in my patients. I suggest visiting the Weston A Price website for more information on how the source of your food affects your health. In short, Grass fed Gelatin is worth every penny people and do not be fooled otherwise.