I've read books by both of them. Yates talks about using one "work set" in which you go to failure, but in reality he did three total sets per exercise (two warm-up and one work set). Yates also favored free weight exercises more than those done on machines.
Mentzer's style was that you did some warm ups before you began your actual sets and that you only do one set to failure, per exercise. Although he used a lot of freeweight exercises, he was a big fan of machine exercises, especially Nautilus machines.
Mentzer also talked about pre-exhausting a muscle group. Take for example a chest workout. Mentzer said that you should pre-exhaust your chest by beginning with flies and then immediately move on to pressing movements. The idea behind this is that during bench presses, your triceps will reach failure before your chest muscles, unless the chest muscles are already more fatigued than the triceps. From what I remember, Dorain liked to begin his workouts with heavier, compound movements like presses.