Obviously both have failed, both rationality and empirically this is easy to see.
Socialism obviously fails because people are evil, they will not help their fellow man and they will not work if they have no incentive to work.
Capitalism obviously fails because people are stupid, capitalism relies on the assumption of competition and a pressure to companies to offer the best for the lowest price. Consumers are completely unable to determine what is the best, and are even dumb enough to buy more expensive products because they believe that once it's expensive it's automatically better, even though there is no indication of that. The existence of crippleware shows that companies often have an oeconomic gain from putting time and effort into reducing the capabilities of their products.
However indices such as the Human Development Index clearly favour countries that lean towards socialism:
http://en.wikipedia.org/wiki/List_of_countries_by_Human_Development_Index
Also, capitalism is often based on the assumption that hard work rewards, I wouldn't say that, the
statistics are pretty clear that the American dream is indeed mostly... a dream... I'd personally say on gut feeling that success is 4 parts birthright, 5 parts damned dumb luck, and maybe 1 part hard work or having a good idea. For some reason, a lot of models in this rule out the 'dumb luck' factor, would Bill Gates be synonym for obscene wealth if IBM just didn't need an OS back then and were willing to take on every-thing so desperate they were? Would Apple and Adobe be huge companies if they just didn't find each other to use postscript? What if the first KFC was just seated at the wrong place and went bankrupt? I'm sure that for every person that became obscenely rich with things like this there are a hundred other people that went bankrupt while they had the same adequacy of business practice, you also need luck.
Of course, fairness set aside, is it better from utilitarian principles? Does it increase the overall wealth to just let the oeconomy be free and let the market evolve as it does on its own. Empirically it seems that this is not the case by a slight margin, rationally, I think the chance of a complex system evolving where you want it to go to is pretty slim, it's like blowing up a block of granite and hoping it turns into a statue. Evolution selects upon the fittest, where 'fittest' in oeconomy is for a great deal determined by 'willingness to exploit the consumer and enrich by leeching from others, not to mention bribing officials.'