This is not a dichotomy. There are a host of possibilities that either include neither of those answers or both of those answers.
I, for one, believe in not fixing what is not broken, but absolutely is. We have a large part of our population that has employer based healthcare that are happy with that healthcare. The problem with employer based healthcare, at least prior to the PPACA, is that people's healthcare was tied to their continued employment creating almost a de facto indentured servitude in some circumstances. That is not in the public interest. The PPACA took a giant step toward unbundling healthcare from employers, which was a good thing. It, for a variety reasons often not by the fault of its design but via political sabotage, did not provide affordable insurance in many markets, leaving people still apart from health insurance.
Though Medicare for All might be a noble long-term goal, its far too disruptive to be considered in the near term. That said, offering Medicare as a private pay option in the PPACA program AND lowering the cost of Medicate eligibility to 50 or 55, which would move the least healthy group off private insurance (lowering costs to private carriers) and make them the most healthy in the Medicare pool (creating a private subsidy for Medicare) would make a lot of sense, IMHO.