Like many of the other Criminal Minds, I've tried both. Early in my writing development, I had these binders I would fill with timelines and tables and character sketches and pictures torn from magazines. I went to workshops where I learned to color-code my prose, to put it on notecards, to use software to organize scenes, to "interview" my characters, and so on.
One of my favorite traditions from that time was one that my friend Lisa and I started. We both had young kids back then, so we had art supplies lying around the house, including a roll of butcher paper and about ten thousand colored markers. Whenever we started a new book, we used to tear off six-foot lengths of paper and spend a day plotting out our work-in-progress, annotating with post-it notes and drawing all kinds of arrows and diagrams and notes in the margins.
Those were fun days. Sometimes we'd go on a weekend retreat and pin those charts up on the walls of the cabin or hotel where we were holed up, and from time to time we'd get up from our laptops and go track our progress against the chart. Looking back on that phase now, I think that - for me - the chart was more of a confidence builder than anything else. It was tangible proof that I had my story under control, that I could reduce it to a flow chart with a beginning and an end and a middle.
I often say that fear is the writer's greatest enemy, and looking back I think I had a lot of fear back then. I was not convinced I could write a full and balanced story, and sketching its skeleton into an outline gave me confidence.
Nowadays, the outline - what there is of it - lives only in my mind. I might make a few pages of notes, but these are very free-form and unstructured, closer to the mad scrawlings of a fevered dreamer than an engineer's careful schematic. That's because I've found something even more addictive than the feeling of holding the reins of my story - and that's the feeling of letting go.
Somewhere between ordinary world and dream world lies this meta state that is a place of intuition, a conduit from the soul to the page, and being in that state is like standing in the violently swirling mist of a thunderous waterfall. You're of the process even if you aren't driving the process - and if that sounds a little organic-voo-doo-y, sorry, I plead guilty.
It's a mad rush, and I could no sooner exist in that state all the time as I could exist on whisky and black coffee, but it's exhilarating as all hell, and it has its place in story creation. It's the place of broad strokes, of first drafts, of shadows of characters whose details can be added later during the painstaking revision process.
I can't say I'll never write from an outline again. I know less and less about the process of writing as time goes on - or rather, it grows more mysterious to me, the more I attempt to learn. But for now, winging it suits me just fine.