Whatever works best.

I definitely believe there is a correlation between the society one belongs to and the choice to have kids outside of marriage or just to not marry in general. In Europe and North America, it can be argued that, the institution of marriage was founded on is false as to how it is perceived today or what successful marriages have turned into. Originally derived around the idea to allow men more legal control over women didn’t sit to well in a society of freedom and liberty for all. Years and many civil rights acts later, plus and ever continuous growth in divorce rate, you have a society that is full of single parent households, unmarried parents, gay parents, etc. This, all going against the traditional view of marriage, because the traditional view, in the sense in which it was applied to society, didn’t work with the society.
The only way being married would be as to benefit a family situation is solely for the legal rights allowed to those who are married and to those who are not. Many people give their vows and don’t stick to them and many people who are in very committed long term relationships who never walk down the isle.