BCAAs consist of the essential amino acids leucine, isoleucine, and valine. That means that they have to be obtained through nutrition because they are not produced in the body. They are also metabolized in the muscle and not the liver, which means that leucine, isoleucine, and valine are available for immediate energy use in the muscle cells.
Study after study shows the importance of leucine as the most stimulating in the muscle cell regarding muscle protein synthesis. So you should opt for a 2:1:1 ratio of leucine:Isoleucine:Valine.