I just took the exam, did all of world and most of rx, and found the exam to be much closer to Rx than it was world. As people said, rx enforces the first aid, but my exam was probably 80% first aid items if not more. World was good for learning, but the test didnt seem like it at all. I guess it made me less prone to get nervous when I got the few crazy out of the blue questions.
Oh well, its over, I recommend Rx.. definately had repeats from that and world. All my biochem, embryo, pharm, micro, were in first aid, and most were in rx in some form or another.