I will only provide you with my personal experiences.....
I took the Veritas Prep Course and found the tests to be an accurate representation of my score.
Veritas CAT 1 - 590
Veritas CAT 2 - 590
What Veritas fails to do is to provide in depth analysis of your scores, pacing, areas of focus, etc. Good measuring stick.
I purchased 1 Book from
Manhattan GMAT - 1 Book gives you access to 6 tests. (1 Book = $25 vs 6 Test = $49)
These were were more accurate at predicting my future score than the Veritas Prep.
Manhattan GMAT Prep
MGMAT CAT 1 - 620
MGMAT CAT 2 - 620
MGMAT CAT 1 - 590
MGMAT CAT 1 - 630
What I love of
MGMAT and what I wish I knew sooner, was that they do analysis on your reports. They can do the analysis by test, by all test, or any tests that you chose. Perhaps you had a bad day and don't want to include that report. The report goes on to show you timing, percentages, and links you back to your actual questions answered incorrectly.
I do know of the others but these are my experiences for both of these.
My GMATPrep Test scores were:
1 - 590
2- 610
Definitely invest and do anything made from GMAC.
Official GMAT Score: 640
Hope this helps!