Don't just think about the work itself but your life outside work as well. Working in McDonald's tends to involve unsocial hours, whereas admin work is typically nine till five. If having evenings free for a bit of social life is important to you, go for the admin job. If it isn't then (unless there are clear career opportunities that might come from one role or the other), simply go for the job with the best money and/or where you'll feel most at home in your work.