http://richardhserlin.blogspot.com/2013 ... le-to.html
My opinion on this is that usually 30 years is too long, at least for most college graduates with a decent income. And if it's a Wal-Mart worker couple, they should be very careful about buying any home they can just barely afford with a 30 year mortgage. The focus should really be about trying to upgrade their skills and education, and especially the education of their children, so as not to be a Wal-Mart couple.
Usually the 15-year fixed is best (and even then it's often best to make additional payments to end it even sooner). The interest rate is lower; the payments aren't that much higher (due to the surprising exponential nature of compound interest over long periods of time – Try comparing the monthly payments and see.), and it so valuable with the country so financially unsecure for families to get to no mortgage as quickly as possible.
In addition, as usual, positional/context/prestige externalities are profound and huge. When a family thinks 15 year mortgage, they are likely to buy a smaller home, not get so much wood, granite, and stainless steel, buy less large and expensive vehicles, etc. But because they get used to that level -- and don't start getting used to a higher level of position, prestige, etc., the decreased utility is not that much, and the increased security of having no mortgage right when the kids are setting off for college can be huge. And in any case, the buying a smaller home, cars, etc., can mean that total payments aren't even higher.