Much of the decision depends on the activity and location (including local laws). I think most would opt for a folder simply because of convenience and legal restrictions. The only challenge with a fixed blade (not a small, pocket-sized one), is how to carry it comfortably, or concealed if applicable. While I would always prefer a fixed blade, they are not always practical or convenient. With that said, I do make sure I carry a quality folder (or three) to do the majority of tasks I know they can easily handle. If I have the option, I would add a fixed blade; in fact, if I was capable of carrying a fixed blade, I would likely have a folder on me anyways.
I distinctly remember an article from "Tactical Knives" many moons ago, where the author used a Benchmade AFCK as a survival knife. While not the most efficient or ideal, the right skill maximizes a small, pocket folder to do far more tasks than most consider appropriate of a folder.
So, for me, it's always a folder, even when paired with a fixed blade, but more likely than not, I will always have a folder on me. If outdoors or on missions, or I can legally carry a fixed defensive blade, I would choose to add a fixed blade to my EDC along with a folder (or two!).
ROCK6