Ballpoint or Rollerball?
The biggest difference between ballpoint and rollerball is not the shape, but the ink. In a ballpoint, the ink is oil-based and tends to smear less during the drying process. If you have a habit of running fingers over recently written lines, ballpoint is probably a good choice for you. Oil-based ink formula, however, causes the ball to be less responsive and some people call it “scratchy”.
Rollerball pens use water-based ink or gel. A rollerball pen puts more ink onto the paper compared to ballpoint pens. This is why writing with a rollerball pen leaves bold vivid lines, but is more likely to smudge.