Who's to say who has the best? In my own opinion, you'd want a GH that is the most complete molecule. In other words, the generics which are 191aa are said to be "almost" complete and don't work as well in the body. Others like Saizen (which I believe is one of the brand names) or Hygetropin which are Pharma grade, have the complete molecule, and supposedly you need less of it to get the same effect as a larger dosage of the 191aa versions. I also have always heard that with taking the 191aa version long enough would encourage the body to product antibodies against it which I've never been able to confirm--take that as you will.
The problem is that we can't really give you a source. All we can do is direct you to what sponsors we have here or on other boards and let you make your own choice.
