Recently, there have been several high profile articles on how writing with pens is much better for the brain than typing. One article presented a study that found: If you write rather than type, you will learn and recall more of the lecture.
For full disclosure, I am a fountain-pen fan and I enjoy the elegance and beauty of writing with the pen. I like writing so much that I have been thinking about converting to a tablet solution (MS Surface Pro 3).
But, as I weigh my options, I cannot get myself to go for a tablet solution or a dual (laptop+tablet) solution. Typing simply knocks the socks off writing when it comes to productivity.
Writing with a fountain-pen has many drawbacks. First of all it is not digital. It can not be easily stored and archived. It is not searchable, and so is not available easily. Most importantly, the writing produced by the fountain-pen is not easily editable. So, this forces you to be extra careful for writing, and self-censor, and this kills creativity.
Let me reiterate this point. The fundamental rule of constructing prose is that you keep the creating (drafting) and editing functions separate. Since editing is hard when using a fountain-pen, you get cautious and blend editing into creating/drafting. And that is not kosher.
Writing with a tablet also has many drawbacks. It is digital alright, but its text (handwritten text) editing is still very clumsy. Copying and moving your handwriting around is harder than simply wrangling text in a text editor. Transposing words, inserting a word in between, deleting a sentence, etc., are hard. Moreover, the tablet is not refined enough yet to give the fountain-pen experience and simplicity. Even the small inconveniences/bumps make your experience unbearable and can keep you away from writing. The tablet is a compromise solution between handwriting and typing. And instead of offering best of both worlds, it tends to offer worst of both worlds.
Typing does not suffer from these drawbacks. The only drawbacks to typing are that the writing looks too uniform. But using a special font you can avoid this. I use the Apple Chalkboard font on my Emacs, and I like it a lot. The Apple Chalkboard font provide some visual differences between different parts of the text. Furthermore, Emacs makes editing text, searching, replacing, etc., very fast that I don't get bogged down when revising my writing.
On Emacs, using the Org-mode offers extra benefits for me. The outline mode is useful for brainstorming and organizing my thoughts and writing. Org-mode is also my GTD tool. I can easily track issues and ToDo lists inside my projects using Org-mode.
So, for me, the choice is clear: Using Emacs Org-mode on my Macbook Air. I am not even considering a dual (laptop+tablet) solution, because using two separate systems for writing inevitably leads to integration problems and complexity. However, I occasionally use my fountain-pen for brainstorming, which I enjoy a lot.