Ah, the age-old question, is it not?
And I hate to give you a horrible, politically correct answer, but I have to: I'm both.
When I was writing my hockey mystery that kicked off this second serious bout of writing (that I'm probably going to edit the crud out of because it definitely needs it), I plotted it out practically to the detail. I wrote out the scenes and some of the dialogue because I was afraid I would forget everything. (I'm the girl who takes too many notes rather than too few because what if I don't write down something important?) Plus, longhand writing stuff has been proven to help you remember things better than typing them out. As a mystery, I couldn't forget a detail either, so it was write, write, write. Plot, plot, plot.
With my pirate mythology story, I plotted out the entire trilogy, but left out lots of details. In fact, I wrote one to three sentences about each chapter. The funny thing was that I stayed with the outline, but allowed myself to waver if need be. And waver I did. The first few chapters were outline-perfect, and then I veered off course... and tied it back together with the outline at the end. I liked that I knew where I was going (honestly, having an idea plotted out motivates me to write, and I can't claim writer's block, either) but that it wasn't as stringent as following every detail of the outline to a tee.
With my supernatural story that I'm currently writing right now, I'm a pantser. I have a a very vague idea of what needs to happen and a loose interpretation of the plot. Other than that, I write everything from scratch. I like this too. It's liberating and freeing and since I don't know what's going to happen next, I find that I'm excited to figure out what happens next. Plus, I am in love with my characters so I feel like we're going on a journey together.
I do like to outline, though. It helps me release my pent-up anticipation of writing the many, many story ideas I have bouncing around in my hand that demand my attention. Once I've written their story out in a form of an outline, they leave me alone, knowing that if I choose to write their story in more detail, I have an idea of what needs to happen for them to be satisfied.
What about you? Are you a pantser or a plotter?