The quality of a system of capitalism, socialism, or otherwise is defined by how well it supports the pursuit of freedom so crucial to the evolution of mankind.
This a loaded question considering the terms socialism and capitalism are defined differently by almost every person you ask and thus have lost their discriminatory value. Also, capitalism (the way we deploy it today) is chock-full of oligarchic socialism, and much of socialism is laced with and supported by capitalism.
The hierarchical dependence on freedom is the key for any system to provide value to human civilization. No system can contribute renewable value to the evolution of humanity without submitting to the relativity of freedom. The freedom of freedom in which the collective freedom acts as the guardrail for the pursuit of individual freedom. Without such relativity of freedom, our evolution turns subprime, regardless of the system of your preference.
Any grouping of people requires regulation and controls to protect the trust and interest in the group (the inescapable paradox of freedom). In a capitalistic environment, the decision is made (by laissez-faire or otherwise) to have the private sector self-regulate the interest of the collective freedom of the group. In the socialistic environment, the public sector guards the protection of joint interests and trust in the group.
The problem with the polarity of either approach is the lack of interaction with the other, meaning capitalism will perform best if it does not treat its participants as modern-day enslaved people to a rat race for money (with sometimes highly questionable socio-economic yield) and on the flip-side extreme socialism without capitalism yields a stultifying downward spiral that is simply unsustainable and unaffordable.
So, the balance between either system is not defined by the fuzzy attributes attributed to each but by how well a system supports the pursuit of freedom so crucial to the evolution of humanity. The most accurate proxy of freedom is not an oligarchically controlled model of freedom we preach to the world as gospel, but a relativity theory of freedom, in which the guardrails of collective freedom defined by every sovereign nation work to stimulate the pursuit of individual freedom (to each his own). And then let the chips of freedom fall where they may.
