What sort of division we pursue is crucial. Many of those maps make their cuts to give each new nation a population equal with all the rest. That has a certain tidiness, but it is politically unwise. Splitting up the union should prioritize and honor regional differences, even if that means ending up with countries of unequal proportions. Electoral maps can be deceiving, but they offer some basic direction in this regard. States need not stay intact, though that would be more convenient for maintaining local governance structures.
On a smaller scale, many of the maps listed above chop up the Black Belt, which strikes me as a mistake. Likewise, while several recognize unique cultural influences along the Gulf Coast, only one notes the concentration of Mormon communities in and near Utah, and none to my knowledge do anything to acknowledge Native American tribal lands. These are the sorts of details a workable split must incorporate.
This may strike you as a defeatist proposal. Perhaps, after nearly 250 years, you believe the union is inherently worth preserving. But what are we really trying to keep? The vague and frankly outmoded idea that “America” is the most important nation on Earth, and must be the most powerful? This is a puerile fantasy. And splitting up won’t undo our history together or cause us to forget our culture. If anything, it might stave off some of the bland national homogenization that threatens to blot out distinct features of our most interesting places. Having, say, seven nations of America wouldn’t make us any less American in any way that really matters.