Who decides the parenting plan or visitation in Michigan?

This is considered by the same people who consider custody, that is, the Friend of the Court, a mediator, or the judge. The same best interest factors are used as are used to determine custody.  Hopefully, the parties “decide” these issues in the end.  The FOC and the FOC referees can only make “recommendations.”  It takes the judge to “decide” an issue if the parties cannot and if the parties (or one of them) rejects a recommendation.