In answer to the topic:
Any system in which there are no major differences between political parties and the various segments of the society (both socially and economically). The more of such differences there are in a society, the more of a class-society you're gonna get, the more people will suffer and there will be more crime. Research within the fields of criminology and sociology backs this up.
Another way of putting it: A system based on a mixture of socialistic, capitalistic and liberal ideas.
Now, there are many different ways of mixing those ideas up, but as long as it doesn't create big barriers between the people living in the Society (politically, socially and economically), it's all good.
The Nordic Model
It's not perfect, but it works damn well.