Hi zharoon,
It's understandable that you would want to work with realistic practice CATs/mocks - and the Official CATs as well as the CATs from Kaplan,
MGMAT and Veritas are all highly realistic (relative to the Official GMAT). That having been said, there are a variety of factors that can influence your performance on your practice CATs that have nothing to do with the 'brand' of CAT that you are using (including the time of day you take your test, how well-rested you are, the environment that you take the test in, etc.).
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) When are you planning to take the GMAT?
5) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich