I haven't taken the real GMAT yet so I can't yet comment on how they compare to the real thing. But personally I find the PowerPrep questions to be the easiest. The new GMATPrep software has very difficult questions, but it appears to score higher, partially compensating. The Kaplan
tests seem to score lower, especially on the math. And Princeton Review
looks like it's in-between, maybe slightly harder than PowerPrep but not much.
So far my practice test scores have been:
PowerPrep 1: 690 (q46, v39)
PowerPrep 2: 770 (q49, v47)
Online: 750 (q47, v43)
1: 640 (q38, v40)
2: 690 (q40, v40)
3: 670 (q39, v40)
4: 700 (q42, v40)
Online: 710 (q48, v40)
GMATPrep 1: 760 (q48, v47)
GMATPrep 2: 750 (q50, v44)
Real thing: ????
As you can see, the quant scores on the Kaplan
practice tests ranged from 38 to 42 (not counting the online version, which isn't a CAT). The scores I received on all the other practice tests in quant ranged from 46 to 50. So Kaplan
seems to be much harder in quantitative grading.
The GMATPrep scores were very high, but the questions were very hard. I made a lot more mistakes on the GMATPrep tests
than on any of the others, but it still gave me a higher scaled score than pretty much anything else. I'm not sure if this is quirk of the software or what. The PowerPrep tests seemed comparatively easy, and I made much fewer mistakes, though the scores didn't seem as inflated.
The most recent test I did was PowerPrep 2, which was 770. Considering the 690 was my "baseline" first test I did before starting studying, I'm hoping that this means I've improved over the course of studying for the exam.
I will let you know when I take the test on Saturday which practice tests I felt were closest to the real thing.