IXLR8,


Chromium is stronger than nickel, bonds better to the brass, but waste treatment issues make it more expensive (these don't apply yet in China...hence the OS clones are ABC.).
The Nikasil like method YS uses is nickel, but unlike ABN it does not peal and it is superior to chromium plating in ringed engines (YS four-stroke engines are ringed).
It also costs more and I don't know of any tapered-bore engine that uses it.