Rollerball vs. Ballpoint
Before you ask someone who writes to talk about their favorite pen, make sure you're in a comfortable position with a refreshing beverage within your reach because you may be in for a long story, filled with more twists than a finely turned ballpoint pen.
Even people who don't consider themselves writers, but spend a lot of time filling out forms on their job, often have a favorite pen. Sometimes it's a promotional pen (mortgage brokers often have the best promotional pens), sometimes it's a novelty pen (that looks like a popsicle or maybe an armadillo), but if the pen doesn't write well, no matter how cute or funny it is, it will end up in the trash.
For those who write a lot, the choice is usually between a rollerball pen and a ballpoint pen. Fountain pen users are totally different breed who often refuse to write with anything else. So what makes a rollerball pen different from a ballpoint pen? Nothing.
It's not the pen, per se. It's the ink.
Ballpoint pens are designed to be used with a fair amount of effort on the part of the writer. The ink used in ballpoint pens is oil-based and tends to be rather thick, so it requires a little more pressure from the pen to the paper, but that's a good thing! Ballpoint pens are suited for most paper types, but are especially efficient for coated papers with a slick surface.
Photo: the "Shelby" pink ivory wood ballpoint pen
Rollerball pens are designed to be used with little pressure. The ink used in rollerball pens is water-based and more fluid than the ink found in ballpoint pens. Rollerball ink flows smoothly, but it can smear on coated surfaces and skip on textured paper. Rollerball pens are great for people who often give their signature or take notes (provided they're using quality paper).
Photo: turqoise stone rollerball pen
As you can see from the photos, the pens look similar and have a similar point from which the ink flows to the paper. One of the things I envy about people who use rollerball pens is that rollerball pens almost always have a cap. There's something satisfying about unscrewing a pen cap - it seems fancy. And if it's fancy, it must be profound.