he USD still remains the leading reserve currency ( is the most widely held). However, central bankers are slowly decreasing their dollar holdings.
In a crisis, people flee to the dollar. This was true in past crises, but I am doubtful it will remain true going forward.
Because nearly every country is printing currency like its going out of style, NO fiat currency is a safe form of holding wealth. Fiat currencies have always been risky. They have become even more risky since the global flood in liquidity. The dollar is vulnerable to devaluation, but so is the Pound and Euro. Putting 100% of one's wealth in Dollars is very risky.
As a side note: Due to rampant printing, money supply has exploded in the Dollar and Euro and Pound at roughly the same amounts (within 10%). That having been said, due to rampant growth in Federal Debt, I think that the Dollar is fundamentally weak.
Who is the biggest printer of them all ?
Surprisingly, it is the Chinese. They have had the largest recent increase in monetary base of all the important currencies. By far, China has printed more currency and has expanded its monetary base much more than the Western Economies.
Surprisingly, the Yuan still remains undervalued and China is experiencing 6-7 % deflation. If the Brits, Europeans and/or Americans printed money like the Chinese, we would almost certainly experience high inflation.