I do a little bit of both. When I'm first starting a story, it's like dragging a 400lb log up a steep hill. It's a continuous and uphill fight all the way. But by the time I hit chapter 4, the story is usually not only flowing, but in some cases even developing faster than I can write, forcing me to drop to a "notes only" form of writing, where I flesh out the plot and sub-elements through a long and complex series of notes, which I then use to fuel and guide the rest of my writing. That's the part I think is hilarious about the way I write. The story starts out kicking and screaming, and before long it's galloping along with glee.
