...for different folks.
I used to be a roller-ball diehard. They were the nicest pens I knew. Now I am an occasional fountain-pen user. I like the fountain pen for taking notes at conferences because they tire my hand less than a ball-point pen and the ink doesn't smear like pencil.
I like having several colors at hand to draw pictures and diagrams with.
I use Bic or cheap pens for much of my scratch work (on recycled paper). Fountain pens don't work as well on some types of recycled paper and I also feel bad about wasting good ink.
I love combinatorists and their endless supplies of colored pens. They always seem to have great colors and some discrimination when it comes to type of pen. They can also always tell you what kind of colored chalk erases best. Some can identify it by the sound when you clink it against the blackboard.
Analysts, by contrast, never seem to think about such banal topics.
Traveling with fountain pen ink is sometimes a bit exciting. One must make sure, if flying in the US, that it will fit into your quart-sized plastic baggie. This is not altogether a bad thing. Once one of my bottles leaked due to the pressure change in the cargo hold. My sunscreen and toothpaste were dyed, but my clothing escaped.