Bitcoin is voluntary, it has value because the global market gives it value. Supply is on a fixed and transparent ledger, the rules are set. New money is distributed by performing work. Based on free market economics.

One is mandatory, it is has value because we are forced to use it to settle all transactions and debts in that currency. Supply is at the whims of central bankers and politicians. New money goes is also at the whims of politicians. Based on Crony Capitalism.