Communism sucks.
Capitalism sucks but is a necessary evil.
Socialism is probably the best, but it only works to a limited extent, and it is easily exploited. Hence, most successful nations are a combination of capitalism and socialism.
The most successful nations in the world (in terms of overall quality of life for the average citizen) are usually small (less than 20 million people), highly competitive, highly skilled, highly socialized, highly taxed, and culturally homogeneous (for the most part). This is why countries like Iceland, Norway, Sweden, and Ireland all rank very highly in things like the Human Life Development Index.
Countries larger than 20 million people usually have to lessen their taxes and social programs to remain competitive with the rest of the world. They also tend to have more diverse populations in a cultural sense, so they spend more time politically in arguments over social policy. Unfortunately, time spent on these socially divisive issues tend to cause lags in economic progress.
So personally, I think population size and cultural conflict have more to do with the success of a society than the economic/political status of a country.