It's like asking which is the best CPU when you discount speed, price and energy consumption.
Nation states need to be able to make huge transactions without any one else holding the currency feeling it. That is what makes the reserve currency the reserve currency.
That can't be done without a massively liquid bond market and no one else is even close to the US.
Then the network of military bases and military power is just another layer on top of the US bond market.
Then on top of that the top competitor has capital controls.
There is signal under the noise of political and military factors
Political and military factors right now are the primary concerns
But in peace time, or with a long enough view (centuries and millennia) the question of what makes a good reserve currency is a question worth addressing