Ballpoint pen dry instantly on paper, but can feel “scratchy” to use and produce a thin and less vivid line when writing. Rollerballs, due to the excess amount of ink it produces, is much smoother on paper, but it can smudge since there is more ink on the paper.
One small downside of ballpoint pens is that they tend to take a bit more effort to write with, but that’s where a rollerball absolutely shines. So if you find that your hand is aching after writing for a while, a rollerball might be the perfect pen for you.