I would say that any of them would be worthwhile, but 3 and 4 are the most like the real thing, in my experience. I took 1-4 and got 220,257,259,259 respectively, with 257 on the real thing. They seemed to be very accurate as far as score correlation, but I didn't really feel like the difficulty was anything compared to the real thing. Don't let the low score on 1 lead you to believe its the hardest though. I took it before studying anything, and the others I took one by one every week until my test day came.