I use pens and I use pencils.
This is a very interesting question. In general I use a pencil if I'm just going to write down a few sentences. And then I go for a fountain pen if I am going to write a few pages. And I go for a very specific fountain pen if I'm going to write a lot (my Lamy 2000).
I also prefer a pencil when I'm going to write on the train or somewhere I don't have a flat surface.
Pencils are fun, but you have to sharpen them way too often for them to be something I can write page up and down with. Kind of the same reason I preferred my Lamy 2000 while studying. Because it had enough ink to last me a full day. Something my Pilot Metropolitan never had.