The choice between a roller and a brush for painting walls often depends on the size of the area and the desired finish. For larger, flat surfaces, a roller is usually the preferred tool as it can cover a larger area more quickly and evenly. Rollers also tend to give a smoother finish when used correctly. On the other hand, a brush is best used for smaller, more intricate areas such as corners, edges, and detailed trim work. Brushes offer more control for detailed work and are easier to manage when painting surfaces that are not flat.