My first principle is this: the essence of writing is rewriting. The media that encourage you to rethink what you rewrite are better choices than ones that don't.
I like that computers and software help create a distinction, even a divide, between rewriting and mere word processing. As we rewrite, most of us do both to varying degrees. The rate at which we can change what we've made visible has a feedback effect of one sort or another.
So while it is easier and faster to execute on a computer, it also feeds my impatience and occasionally helps me make fast decisions at the expense of a better one.
Sometimes I want to feel what I'm writing, which calls for a typewriter. Sometimes I want the sense of what I'm writing to burn into my memory, at which point I write on paper. Sometimes I want to carry around something in a notebook, not a file folder.
I suppose what I am speaking to here is the act of writing itself as a multi-dimensional experience. I vote for all of them; each one is a means for self-discovery.
My last word on word-processing: if what you've written or machine-typed really needs to get to an electronic form, you may be utterly surprised at the effect of someone else typing your words in has on you. I urge you to try it at least twice.