Up until the mid-1970's I'd actually say Yugoslavia. As they were not part of the Eastern Bloc, they were in a lucrative global position: getting financial, economic and military support from Western countries, Yugoslavia was economically far, far better than the other Communist countries. Blimey, they were eaven working on a space program and partially sold their raw materials to the United States in exchange for economic support. Plus, Tito managed to make Yugoslavia the centre of the Non-Aligned Movement, which boosted its credibility among the Third World. Throughout the Fifites and Sixties, China was basically an unstable and fanatical country torn by the Great Leap Forward and the Cultural Revolution. And they got a pretty bloody nose while fighting against Vietnam in 1979. But that year was also the turning point: Deng rose to power, whereas the economic decline of Yugoslavia started.