Hydrolyzed collagen is the same collagen found naturally in bones, skin and cartilage. I chose this product because my friend who does much research and study on the products she takes and she told me about this. I also read the reviews on the site I purchased the product from and they were mostly positive.
As a consumer, I think that they are pretty much the same thing with the difference being bio-availability. Gelatin is a food stuff, made by boiling bones of beef, usually, but any animal has collagen in the bones. It is a mass of tangled proteins that gels upon cooling. Collagen hydrolysate is supposed to have a more thorough processing that breaks the collagen into smaller pieces (amino acids) that are hopefully better absorbed. I would try both and see which one works best for you for the price. With straight gelatin, it would be difficult to determine how much of the different types of collagen you are getting, however, not knowing what you are looking for, that might be okay in your case. Here is a link to the webmd supplementation for gelatin/collagen hydrolysate. They make no distinction between the two. http://www.webmd.com/vitamins-supplements/ingredientmono-1051-gelatin.aspx?activeIngredientId=1051&activeIngredientName=gelatin&source=1 And here is a link to genacol mentioning different types of collagen. http://www.genacol.com/en/content/26-roles-of-collagen-in-the-human-body Hope that helps.
I'm not a scientist but the difference is in the size of the molecules of collagen vs. gelatin. There is a pretty definitive answer on this website: http://www.gelatine.org/en/about-hydrolysed-collagen.html Sorry I couldn't be more help but that's the best I can do. I chose the collagen vs the gelatin on the recommendation of a friend.