I only use pens when the task at hand requires permanency – ie, to write a check. I find pens an inferior way to transcribe thoughts of any kind to paper. I think this is probably because the majority of the writing I do on paper is rather free-form. I am a doodler and visual thinker, so I tend to take notes in a very non-linear fashion and often am doing sketching intermingled with my notes. UI mockups, model diagrams, etc.
Pencils are the clear winner for this type of interaction with paper. Not surprisingly, I also do all this note taking in unlined artists’ sketchbooks. The richly textured paper interacts with the pencil lead in a pleasing way.
I would theorize that people who prefer pens tend to be people who do more pure text writing on paper, and would also tend to be the types to use lined notepads. Any truth in this assertion?
At any rate, I started this because I also wanted to share my weapon of choice. The Pentel Twist-Erase 0.9. It has a slightly larger diameter than many mechanical pencils, which suits my large hand, the twist out eraser is high-quality and genuinely useful, unlike those on most competitors. And the 0.9 lead is a must. If you are a person who has sworn off mechanical pencils because of the constantly breaking leads, you probably haven’t used a 0.9.