I know people say that Kaplan's huge curve makes up for the difficulty, but I would have to disagree. I consistently score 2-3 points higher on AAMC's. I have not topped 32 on a Kaplan but have a max of 35 so far on AAMC (10).
Oddly, everyone says that Kaplan exams after the first 5 are soooo much harder that they completely desecrate your scores and are not representative, while the first 5 Kaplan exams are. I have noticed a similar trend: In ALL Kaplans, I score 2-3 points below AAMC average. I took Kaplan 9 yesterday and got a 32. Today I got a 35 on AAMC 10.
Kaplan PS pretty much rapes you, but as long as you go over the explanations well, you'll pick up a lot of info.
But DO take ALL AAMC's. IMO Kaplan should be mainly used for review and troubleshooting. Space them out so that you're using Kaplan to brush up on weaknesses exposed in the AAMC's.