In which form of municipal government do voters have the most impact on the executive branch

I would argue that the voters have the most impact on the
executive branch in a municipal government that runs on a strong mayor system.  There is
much more impact in this sort of system than there is in a weak mayor system or, even
more, in a council-manager system.

In a strong mayor
system, the voters get to vote directly for a mayor who has a great deal of power over
the executive branch.  This gives the voters fairly direct impact on that branch.  By
contrast, in other systems of government, the executive branch is run by unelected
officials like a city manager.  These forms of government do not give the people nearly
as much direct impact on the executive branch.