Branched-chain Amino Acids or BCAAs are small, individual units that become "chained" together and that sometimes have side chains that "branch off". These Amino Units come together to form various chains that eventually create Proteins.
There are many Amino Acids, but there are only 3 BCAAs - Leucine, Valine and Isoleucine.
All BCAAs are Essential Amino Acids or EAAs, but not all EAAs are BCAAs. There are 9 EAAs and 3 of these Amino Acids are BCAAs - Leucine, Valine, Isoleucine.
EAAs are called "Essential" because your body can't make enough of them to meet its demand or it can't make them on its own at all.
Because of your body's inability to make EAAs on its own, you'll have to make sure to consume enough EAAs to fulfill your needs and achieve your intake goals.
Taking a Leucine Heavy BCAA Supplement can
Leucine, the "Star Amino", is by far the most important BCAA for Stimulating Muscle Growth.
Leucine is most responsible for activating a complex process called mTOR, a process that increases protein synthesis and muscle tissue growth.*
BCAAs can be found in many foods and it's not too hard to get a lot of BCAAs from your food.
However, food has to be broken down in the gut then make its way through the liver in a time consuming process that's not terribly helpful when you're trying to Fuel Your Workout Now!
Direct Supplementation of individual BCAAs through a High Quality, Leucine Rich BCAA Powder Drink Mix allows these three EAAs to be quickly absorbed by bypassing both the gut and the liver.
Faster absorption and availability of Amino Acids floods the muscles with the BCAAs You Need When You Need Them!
We already know that Leucine is the Star, but supplementing with just Leucine can lead to a BCAA imbalance that doesn't maximize results making it important to supplement with all 3 BCAAs. 
If Leucine is the most important BCAA, but you need to supplement with all 3 BCAAs to Maximize Results, don't you want to get more Leucine than anything else?
For the Best BCAA, look for a BCAA Ratio that includes all three BCAAs, but that is high in leucine, like an 8 1 1 BCAA ratio or a 12 1 1 BCAA ratio.