Thanks to Empower GMAT's killer methodology, I ended up with a 730 on the GMAT, up from my earliest Veritas test scores of 620.
Empower's methodology for each and every type of question is what I found really helpful - Instead of being template driven they teach you to approach problems in a certain way, testing and cancelling choices. They even coach you to read properly, since most people have bad reading habits for the GMAT.
Their methods really worked for me both in Verbal and Quant. A video library of solved OG13 questions really helped.
I worked with Veritas Tests and got 670 average prior to test day, when I got 730. Do note that Veritas tests are good on content but not accurate at score prediction (in my case). I studied for 3 - 4 months after work, for 1 - 2 hours daily.