Capitalism rewards people who increase the value of their labor (more education, personal risk, etc.) and people who risk their money. As we all know, people don't always start at the same point due to genetics, culture, wealth or whatever. Monopolies or near monopolies don't help the gap (and are likely to form in pure capitalism) because they can control large percentages of wealth with their existing wealth and power.
On the otherhand...
Socialism is more beneficial to people with low valued labor. There are decreasing rewards for working beyond what is required or taking risks. Instead of monopolies holding power/wealth, the government usually holds power/wealth. Wealth/benefits are generally more balanced, but business is usually less efficient because of lack of incentive and competition.
I'm sure I forgot plenty, but its 2:00 AM. I personally think that a mixed economy that leans towards capitalism is nice (a little more capitalist than the US). Lots of social benefits suck IMO (aka my family pays about 50% of our income in taxes in Texas), but there are some I think are important: education (it should go to college level; not highschool), limited unemployment benefits, but I don't really care for health care, particularly for the elderly -- they need expensive health care that generally doesn't allow them decent quality of life. My biggest issue that I can think of atm is that large corporations have too much control over the government. Their power needs to be more limited in order to ensure competition. Also the wealth gap still sucks, but I have no idea how you could get rid of it in a more natural way than giving everyone other people's money; someone else can figure it out.
That's kinda my 2:00 AM stance. I'm sure I make plenty of generalizations and say some ignorant things, but I'm also human. I also left out a lot of stuff such as private/public property and freedoms, but there are so many facets it's unreal.
Communism is completely different idea that actually sounds nice, but I wonder a truly classless society would continue to progress or if it's even possible given human nature. I would be happy to be proven wrong though. I don't think that a centrally controlled socialist government could ever achieve it; however, because the government simply controls too much power.
EDIT:
What is this risk that I apparently believe in? Land renting seems like the least risky business imaginable.
It ties up money (and is hard to sell sometimes, especially if people are renting it), you have to pay taxes on it and people might not want to rent it or be able to pay when they do. The property value could potentially go down. I don't think the risk is particularly huge, but the profit made from it probably isn't that great either in comparison to other more riskier ventures unless they do some real bullshit like they used to do (force farmers to buy supplies from their stores, etc.). All speculation, but anything that you invest money in isn't devoid of risk.