In thinking about how best to respond to this question, I decided to compare my writing and speaking not in strict, exact terms regarding grammar, diction, complete sentences versus phrases, proper use of tenses, etc., but rather in terms of the spirit of communication as a means of connecting with others.
My answer, then, would be that my writing is very similar to my manner of speaking. For one thing, both the writing and the speaking come from the same brain. I think, therefore I speak. I think, therefore I write. I think, therefore I am.
When I first began to write creatively or, at least, purposefully, I made a conscious effort to be perfectionistic. Now, I just ramble in my writing just as I do with my speaking. Allowing a body of water to flow naturally is better than making like a beaver and damming the aquatic resource.
There's also a zen quality in my writing that links to my speaking. When I write, I pretend that you or so-and-so are sitting at a table in a coffee shop or on the steps of my front porch. I let myself be one with that image and find that it enables me to simply flow with my (written) conversation. That's why I never use outlines in my writing...I simply talk to (the collective) YOU.
Thanks for asking a question that's both simple and profound. See you 'round the bend, rutley!