The question between socialism and democracy as economic systems is whether wealth should be distributed by need or by ability. When distributed by need, populations tend to become less productive. When distributed by ability, the distribution of wealth becomes unequal. Capitalism has surely been the most successful economic system in terms of survival. Socialized economies have declined considerably in the past forty years.
As political systems, it is a much more difficult to make such a judgement. World-wide, there is so much diversity in political systems that it is near impossible to define individual systems with one label. Almost all have some form of voting. In some countries the vote is meaningless while in others it is effective. In general I would say democracy is the most successful simply because there hasn't been any revolutions in truly democratic countries.
