With physical currency, gold is the leader, but there is also silver, important because it has a high commodity value from silverware to batteries (to film back in the day), and you need both. And then there are less used metals like platinum (hard to work) or copper. Notice that original US constitutional currency had gold, silver, and copper. This has been the case for thousands of years.

If you want an arbitrary analogy:

Bitcoin = gold

Namecoin = silver (provides globally consistent namespace)

Pktcoin = copper (provides metered income from amateur internet links)