I personally perfer a mechanical pencil. The problem with these bastards is that they always seem to break. I happen to have had the good fortune of using these things since I started writing my name with out someone telling me how to spell it, so I'm able to fix them.
I like pens, they're reliable, but they just don't get it done in my opinion. To quote a cliche, pencils have erasers because man is not perfect. So why would I want to constantly write with something that is unable to fix said mistakes?
Wooden pencils with graphite are the original. They were around way back in the day and they're still used widely now. I actually went two semesters using only 8 wooden pencils and i made it through alive. But i hate them. They never stay sharp, so I had to keep a pencil sharpener in my bag, so that got full of partial pencil shavings... pain in the ass. And the erasers seem to disappear faster than free liquor at an AA meeting. I can never seem to keep an eraser on those things and when I try to put one of those pink erasers on the end, it ends up falling off somewhere along the line and then I'm screwed.
I just stick with mechanicals. sure they break or get jameed, but the eraser is always there and I never have to worry about it getting dull.