My general inclination is that secretaries should report to an administrator, if there is one, because that person can handle coverage issues, workload imbalances, and squabbling. The lawyers (and perhaps paralegals) they support should contribute significantly when it comes time to evaluate the admins’s performance and certainly direct them day to day.
Paralegals, in contrast, should report to the lawyer whose work they support, and dotted line, perhaps, to an office manager for some administrative matters.