I must say, I have trouble aligning myself with one or the other.
Some time ago, I was still convinced am an absolute pantser. Just go with the flow, let the characters make their decisions, see where it leads. And while I still give my characters a lot of leeway, I have backdrop and myths and relationships and childhood stories in the back of my head worth hundreds of pages alone. So in one way or the other, these things find their way into the active narrative.
But not without me planning the bones of the story. I definitely need some kind of outline, and it does make things easier. Going in without any plan might be nice when you are prepared to do a LOT of editing later. But even with a plan, you will still be faced with themes that jump at you at the end that you didn't quite see when you first started out. And then you need to cut back and expand where it's necessary to emphasize these themes.
So... better have a mix of both. Go in with a basic plan, build your world, but let your characters explore and don't be too hard on yourself when things change. Chances are, they change for the better because you have a better understanding of your story.