If the government is going to favor one household/family structure over all others, I reckon that the official family of the United States should be the matrilineal extended family with visiting spousal relationships ("MEF-VS"). The nuclear family is just too unstable and problematic, and I don't reckon that it's sustainable in the long run without considerable subsidies. I'm not saying that you shouldn't be able to live in a nuclear family, just that the government won't recognize it in any tangible way. And self righteous blowhards will criticize you for your immorality and selfishness.
Here's a snapshot of how the MEF-VS would work ideally. I'll take my own family as an example. My mother, who is in her late 60s, would be the cornerstone of the household. Her oldest brother, my uncle WE, who is 90, would be the titular head of the household. He would visit his wife and children from time to time but reside mainly with his sister and the rest of the family. His younger brother, my octogenarian uncle GH, would also live in the family compound. He's a widower who was childfree, so he would be around most of the time. I would have been raised by my grandmother, her brothers, my mother, and her brothers. My father would have visited periodically and sent cards and gifts and what have you but would have lived with his sisters and raised his nieces and nephews. I would be the heir to my uncles, and my sister's children would be my heirs. My sister's son would be next in line after me to be titular head, assuming that I outlive my tireless uncles. My sister's grandson would be next (he's only 3 years old). We don't have a lot of females in the family, so our compound is a little heavy on the male side.
Let's take Mrs Vache Folle's family as another example. Her mother is one of several daughters and only one son, her uncle Joe. Aunt TM would be the female head, and Uncle Joe would be the male head. The sisters and their children would all be part of the compound. Their husbands would be frequent visitors, or not so frequent as the case may be since they are all past their childbearing years. One or more could go off on their own to start a new sublineage if it seemed right, but Mrs VF's matriline looks as if it will go extinct after her generation which had only sons.
The ideal MEF-VS, given the preference for two child families with one of each sex, would be more like my own after my uncles pass on since we have three generations of perfect boy-girl reproduction. The advantages of the MEF-VA are manifold. Marriages would have a lot less pressure on them. They would fall into a sexual rut much later since the spouses will not live in the same household but will be in a perpetual dating/booty call situation. Women would be in a greater position of power and influence within the household as they would never be called upon to live among strangers or apart from their birth families. They would have the protection, if they needed it, of their brothers, uncles, and nephews, and other women in the matrilineage who might be also ass-kickers.
Other advantages would be that families would pool their resources over two or more generations and could share responsibilities for childrearing. Talk about a social safety net! The expense of maintaining distinct households in nuclear families would be saved, and families would have more savings and the ability for family members to leave the work force more easily to care for children and the elderly.
The nuclear family often degrades into a divorce with a visiting ex-spouse (who visits the children only) and the added expense of an additional household. This leads in may instances to step-parents, whom we all know from fairy tales are almost universally wicked. This is not nearly as stable, healthy and satisfying for children as the MEF-VS where they are surrounded with loving uterine kin all their lives.