Class
I went to Bill Phelps in Phoenix for both. See my post under the ALL ATP Bad Experience thread. I got much more out of going to class than I ever did studying at home. I studied for most of my pre-ATP writtens at home and went to class for Instrument and II.
I would opine that it all depends on your learning style. No matter how motivated you may be, it is hard to sit down at home and study. It is easy to find excuses not to study, especially after working all day. With class, you are fully immersed in the subject. You also benefit from the interaction between teacher and class.
That's my .02. Good luck with your exams.