The Open Government Data (OGD) movement has seen governments around the world embrace the concept of opening their data. However, the large amounts of data released have not resulted in wide acceptance of the data by end-users. This is partly due to the emphasis on machinereadability rather than human-usability. Recently, some data portals have included visualization techniques to make the portals more usable. In this work, we report on user studies conducted to evaluate different OGD visualization techniques. The techniques were evaluated both quantitatively, through recorded tasks, and qualitatively, through a post study survey. We found that geographic map visualizations were reported by users to provide the highest level of qualitative satisfaction, which correlates with the quantitative results requiring the shortest time to complete the tasks. This study provides insights into empirical evaluation of visualization techniques to aid OGD providers in making decisions about the best way to present data in their portals.