Well then yours makes even less sense cos nowhere is cupro-nickel anywhere near as important as silver (or not as the case may be, cos i'm not sure which way round you've put them). I'd say copper was better than bronze, and copper/silver better than bronze, cupro-nickel and nickel-brass put together. I'm a purist, i like my metals pure, the purer the better. It's all very subjective that way though cos i would list them like this; most important to least (interpret expensive to cheapest, in general terms, high grade nickel-brass coins tend to cost slightly more than cupro-nickel ones, only cos some of those threepences are scarce though)... Silver, Copper, Bronze, Nickel-Brass & Cupro-nickel.