Compare Vietnam, China, Laos and at best Cuba, to the rest of the world to see why. Capitalism has it's faults, but can work with them. Watch this video and see why Communism all though on paper works, in practice fails.
(Oh, and let's not forget the lack of freedom and innovation with Communism).
The whole system of Communism is built around a totalitarian dictatorship, and as the saying goes, absolute power corrupts absolutely. Inevitably, the system will become rampant with corruption, which abuses the workers and silences decent, and the stealing of property by the government. Free speech is destroyed and political opponents are arrested. And, as an ultimate irony, it exploits the poor workers in favor of the party and its powerful members; the ultimate hypocrisy. Capitalism, however, gives individuals the freedom to control their own lives and pursue happiness as they see fit.
Capitalism is a system that produces more money. Even if the world were to see pure communism, it would not be comparable to capitalism. That is because communism is not built for profit, it is built for fairness. If we were to compare the quality of life of both, communism wins. Capitalism provides the opportunity to be a very rich man, but also the opprutunity to be destitute. It is hard to answer a question like this, because we have only seen individual totalitarian governments, instead of a single, worldwide government that is strong, but fair.
An unregulated economy leads to better results. Leaving people alone will cause them to naturally invent things and work for money. People don't work under communism because they get money no matter what they accomplish. We are not all the same and should not be given the same amount of money.
I'm not someone who sticks with a side (left or right) when talking about politics, as I think different questions demand different solutions, regardless of the political position these come from. However, I consider myself to be a centrist when it comes to the economic axis because, in my opinion, both government and corporations are inherently evil by the very human nature of ambition for power, and as far as I understand, communism and capitalism are two ideologies that, in their most pure form, demand for each of them (respectively) in excess.
That being said, I believe the best we could ever achieve as human beings and as societies is something called a "mixed economy", which is an economic system that takes points from both sides (capitalist and communist) and put them into action, balancing powers between a government and plenty of corporations. That economic system can be found in basically every country in the world today, as there's no such thing as a purely capitalist or communist country, but as I see, nations such as Canada, Norway, Sweden, and Finland (as well as a lot of other delevoped countries) seem to follow it better than any other country.
But as I am being demanded to choose between capitalism and communism, I'm going to pick the former because, although it has its issues, I think it is the least worst option of the two and it's the only one that was able to "make it to the 21st century" without collapsing or surrendering to tyranny (in most cases, just to be clear), and also because it values meritocracy (hard work) and individualism, which is a key part of democracy (and thus an important tool to avoid tyranny and opression by either government or corporations) and is an efficient way to solve problems, by letting individuals be free to solve questions brought to a society in their own ways, and making it easier to conciliate and understand each one's opinions instead of silencing what each person thinks and says in favor of a bigger group (collectivism).
Defining my terms to be in economic efficiency and the amount of goods and services produced. In capitalism, every person is motivated to work and invest in order to produce profit. Now, profit is generally seen by the left as an evil, yet it should be noted that profit comes out of voluntary exchange, and any voluntary exchange must help the two parties that conduct this exchange (otherwise the exchange would never have occurred). But the most simple argument is that capitalism rewards people who help others (by giving others things that they want, others will give them things that they want, this is known as trade), whilst socialism redistributes wealth and lacks incentive to work, invest, trade and other activities which are beneficial for society.
The people who are pro-socialism or pro-communism often talk about the "exploitation of the weak". However, one must first define what they must mean by exploit. The argument of the "exploitation of the weak" cannot mean that the "weak" do not gain from this so called "exploitation", otherwise they would never have conducted the exchange (whether of goods or of labour) as all exchange in a capitalist society is voluntary. So, the "exploitation of the weak" argument must be stating that the "weak" benefit yet don't get a fair share. But if you create any law that tries to limit what the market can or cannot do, this will inevitably result in people leaving the market due to their lack of benefit (whether it be the producer or the consumer), and will create deadweight losses in which the market creates less resources than it otherwise would. Thus, the decrease in incentives to engage in mutually beneficial transactions leads to less goods/services provided, and thus leads to a decrease in the average quality of life.
I must also further ask one thing of the pro-communists or pro-socialists. Is there any logic in what they are saying? Can they provide a logical reason for why their society will be more efficient? Can they provide a logical argument why the redistribution of wealth will motivate people to work more (and I provide the argument that it demotivates people to work more, as it reduces the gains and losses, and thus the incentives to work)? Or are their arguments simply based on ideals and wishful thinking, and just simply employ meaningless words and phrases such as "unfair" or "exploitation of the weak" to try and support their cause.
Left to its own devices, the free market will inevitably fail, and as we see constantly in the world around us, mixed economies fail too. This may be attributed to the flawed nature of capitalism, which is centred on 'every man for himself', profit maximisation and the exploitation of the weak. The upper income brackets of developed countries continue to not pay any taxes, refusing to redistribute wealth to those stuck in the lower rungs of the social ladder. With rigid economic planning, the abolition of private property and social cooperation, communal prosperity can be achieved. Workers of the world unite!