Best ECM dedicated helicopter!!

I am contemplating on the best Electronic Counter Measures helicopter. Is your choice a Western derivative or an Eastern Bloc one?? My knowledge in this field is relatively weak so I really cannot give an example without “backing it up” with information. I know that the russian Mi-8 ECM is a typical paltform but is there anyone who can elaborate on the US Blackhawk version or even on the South African ECM Oryx. Any information is greatly appreciated!