I don't see why there can only be one, before the crime of 1873, the US happily used both gold and silver as monies.

Also gold and silver are never going to go away as ornamental and industrial materials which ensures continued demand and thereby at least some viability as a store of value. None of them enable you to trustlessly send small amounts to the other side of the world in an instant so they'll never be able to compete with bitcoin online because a digital IOU on some hunk of metal in someone else's storage just doesn't cut it.

When my friends ask to buy bitcoin off me, I tell them I only sell for precious metals because I think they're equally viable.

So what I'm trying to say is bitcoin and precious metals complement one another and any competition between them is entirely unnecessary.