In short: Gerry Grossman by far.
First off, the people I've talked to all said that the practice exam test bank questions were the most helpful part of the exam prep.
AATBS lets you use their testbank questions for only three months! Gerry Grossman lets you access their test questions for an entire year. AATBS did not make it very clear that they had a three month policy. I've talked to others who were surprised and angry about it after already paying the $700 to $1000 fee.
AATBS has less practice exams than Grossman for both the written and clinical vignette exam. I think the AATBS written exam has five or six sample tests and Grossman has nine. Since most of the exam prep involves taking and retaking lots of practice exams Grossman wins here too.
AATBS questions seemed to have a lot of quality control issues. A lot of questions were confusing, unnecessarily difficult, and ended up being less helpful than Grossman for getting a feel of the actual exam. Especially for the cinical vignette exam, AATBS test questions were extremely confusing and people I've talked to say they learned very little from them. Those who used both methods relied almost exclusively on Grossman.
Some people thought the actual exam was harder than the Grossman practice exams and some thought it was easier. For the clinical vignette, however, everyone I know thought it was more confusing than Grossman but less confusing than AATBS.
One person said they thought AATBS had better study books than Grossman. Like I said, I thought the study books played a small role in the actual exam preparation process.
I haven't heard a comparison between Grossman and AATBS on their workshops so I can't speak to that.
If you had other experiences please leave a comment.
Hope this helps!
