I rarely (maybe 2-3 times a year) eat at a fast food restaurant but to answer the question I would absolutely choose Burger King over McDonald's. Burger King has better fries and their burgers are just as good if not better than Micky's.
The last time I ate Micky's fries, they tasted really good when they were warm, but once they cooled down had a chemical flavor and got all hard and yucky and didn't even taste like potatoes. Never went back again. When I was growing up McDonald's was "the place" to go and we only went on special occasions and I really liked them back then, but now I think they just went down the tubes.