I usually do after. But thinking about it for a moment, it makes more sense to do before. The order should be; floss, brush, mouth wash. Makes sense to me!
I floss after brushing. I think I do it after because when I go to the dentist to get my teeth clean, they do it after my cleaning.
You gotta floss after brushing in order to get what's left behind. That way the flossing is enhancing your brushing and not they other way around!
Before brushing because I want to get the old stuff out from between my teeth and then give the opportunity to clean with toothbrush. Not only that but when I use mouthwash I can clean in between the teeth better if I floss before everything. Floss, mouthwash, brush always.