Unfortunately, there seems to be no consensus on which is the highest yield study material for step 2. However, from reading a lot of posts at various websites, hearing different opinions from other test takers, and from my own personal experience, I would say that for steps 1 and 2, it seems that First Aid and B&W are respectively the highest yield study material available for these two exams.
These books generally should be supplemented with question sets (NMS, Q-bank, and perhaps Mock step 2 if time permits) to get your mind tuned to skimming lengthy clinical vignettes for the diagnostic or management pearls which will save you time on test day.
As an added note, I have also heard that Swanson's Family practice is the single highest yield source of review material for Step 3.
Good luck everyone.