Is bigger EU economy, US economy or China's economy by GDP ?

I have seen a rankings of world economies by GDP and in some of them, there were a different positions of EU economy, US economy and Chinese economy. Which of these economies is bigger ?

There are different positions of EU economy, US economy and China's economy in the rankings, when the countries are ordered by Nominal GDP and GDP PPP. These two approaches are generally used for different reasons. PPP is an abbreviation of Purchasing power parity.

The largest economies by Nominal GDP in 2018:
United States - 20.54 trillion USD
European Union - 18.77 trillion USD
China - 13.61 trillion USD

The largest economies by GDP PPP in 2018:
China - 25.40 trillion USD
European Union - 22.45 trillion USD
United States - 20.54 trillion USD

The values above are approximate. Purchasing power parity compares standards of living and economic productivity between countries.