I recommend Getting to Maybe. But I'd be cautious about any particular exam writing "system." The main thing that Getting to Maybe teaches you is some organizational techniques and to be sure to argue both sides. You should really base it on the professor, the specific question, and the grading.
Does the professor want a cohesive, structured essay or should you be writing stream of consciousness and making lists to get the points? Does the professor want you to spot every issue or just focus on the important ones? Should you be writing a normative /policy essay? Some professors like clever jokes and others hate them. After reading essays my classmates wrote, I will tell you one thing -- about 10-20% of the people in my class wrote using inappropriate tones. If you're writing like an attorney from television, chances are you're writing badly. If you're using words like "Clearly", "obviously", you're probably not writing well. I'd steer away from first-person and overly informal tones.
If you don't have the divination skills to figure this out on your own, a good technique is to ask the professor (and compare the answer with what you get from other students who have taken their class).