Honestly those first two are gonna be pretty much mutually exclusive. In the US. San Francisco and NYC are the only places I can think of that you can reasonably get around on public transportation.
Boston is pretty good too, enough of the city predates cars that it's decently walkable, and the T isn't terrible by US standards, they even got some new trains in the last couple years. Very very expensive but cheaper than nyc or sf.
Honestly those first two are gonna be pretty much mutually exclusive. In the US. San Francisco and NYC are the only places I can think of that you can reasonably get around on public transportation.
Boston is pretty good too, enough of the city predates cars that it's decently walkable, and the T isn't terrible by US standards, they even got some new trains in the last couple years. Very very expensive but cheaper than nyc or sf.