Socialism has never been sustained is the problem.
But....
Russia after 1917 revolution, turned communist= Became a superpower.
However in 1989 I believe they collapse.
China, taken by the Communist party, Economy booms crime rate greatly reduced.
Cuba, established dictator under communism, Cuba is one of the richest countries in the Caribbean.
Socialism can be democratic
Communism cannot
So to answer your question...Cuba.
The U.S. thinks if it keeps the embargo that Cuba will become capitalist.
It failed.
Socialism always brings a country up...But has never really been shown to withstand the test of time.