Using circular shaped brush over rectangular for painting

There is a brush tool inside a semantic segmentation AI tool that I am working on. The brush that is used currently in a rectangular shape. Now while doing UX testing of that tool I realized that painting using a rectangular brush makes the overall strokes look pixelated. As you can see in the image.

While painting with a circular brush will obviously give smooth edges like the other picture in black strokes. Rectangular brushes are good if you are painting perfect rectangle shapes.

Our case is similar to painting over an object and smooth corners will obviously make the painting more accurate.

What I wanted to know is specifically what are the positives and negatives of using both types of brushes. You can see the third image to know how semantic segmentation painting looks like.