Real GMAT: 660
Kaplan: 540, 550
GMATPrep: 690, 660
PR: 610, 590, 540
Obviously, the GMATPrep scores were the best indicators...as everything I had read prior to taking the test also verified for me. Kaplan scores are low for everyone...mine over 100 points lower than what I actually got on the test. My Princeton Review scores were frustrating (note the downward trend), but those were the first three practice tests I took and I was much more confident after doing the GMATPrep tests. Hope this helps...best of luck to everyone preparing for the test.
Real GMAT: 660
PR: 610, 590, 540
Kaplan: 540, 550
GMATPrep: 690, 660