Transit agencies periodically assign each of their drivers with a shift describing when and for how long they will work each day in the following months. Since drivers are not indifferent to which shift they receive, transit agencies define different assignment methods often based on driver seniority. This article studies and compares different shift assignment policies assuming that the agency has some information regarding the approximate utility that each shift represents to each driver. Additionally, based on a study that analyzes driver utilities for flexible shifts (i.e. in which the weekly number of hours is not distributed uniformly along weekly working days), it shows that implementing flexible shifts offer a win-win opportunity for the agency and the drivers. On one hand drivers improve their productivity (i.e. fraction of the time in which drivers are actively working); on the other they increment their satisfaction with their job. This is particularly relevant since transit operational costs are strongly dependent on their labor force. Some of the benefits obtained by the firm should finally be captured by the users of the system.