For the first draft, I prefer handwriting with a pencil and paper. The most important reason for this is that I am more creative and productive with this method. The second reason is that I can avoid distractions when writing because when sitting behind a computer, notifications are really disturbing. Even if I turn the network off, as a computer and software nerd, I have the temptation to do many hacking and tweaking on my computer and forget about my main task, writing. The third reason is that it can prevent me from jumping from writing mode to editing mode because editing a handwritten draft is not easy. From the day I changed my writing habit from typing in a computer document to handwritten document on paper my productivity improved significantly.
As for using a pencil instead of a pen, it is because my brain works a bit faster than my hand, in a way that when I’m writing, I frequently omit letters from words and write the next letter. So I keep an eraser handy to correct these types of errors to the point that it can’t be called editing. It may be some sort of disorder, but I’m getting on with it.