GMAT Club CAT vs GMAT Prep

I don't know much about the GMAC CAT mocks, so I won't comment on them specifically, but the only mock tests out there whose scores are actually worth paying attention are the GMAT CATs. They’re written by the same people who write the actual GMAT, and they’ve also been statistically tested and selected on thousands of students, so you know they’re realistic. Next, they’re the only mock tests out there that are adaptive, matching the questions you see – just as the actual GMAT does – to your performance.
However, taking any test in order to “know where you stand” misses the point. Your score on a practice test is a nice bit of gossipy information to share with friends who are also studying, and if you did well, brag, by all means. But this isn’t the point of these tests. The reason to take mock tests is that they are a vital part of your study and improvement process.

If you have any additional questions, fell free to ask me here