I'd say American law enforcement, with it's resources, experience in organized crime investigations, RICO, the witness protection program, etc. is the most prepared to confront emerging crime groups and prevent them from becoming entrenched.

We also have to remember that it often comes to an agency jurisdictional thing. The FBI investigates the LCN, as well as the Russian, Asian, and Balkan criminal enterprises. The DEA is the agency that goes after the purely drug-trafficking groups the most, i.e. the Mexicans, Colombians, etc. Although there is obviously some overlap.