First of All, I am really grateful to everyone who has shared his or her experience on this forum. The advises and suggestions I received were paramount during my three weeks GRE preparation. Having said that, I believe it is incumbent upon me to share my personal experience as well.
I spent around 70% of my time studying for the Quant section as I intended to apply for a math intensive field and therefore couldn't dedicate much time towards the verbal section. I started out with Manhattan 5 lb book (completing the math section in one week - all ~30 chapters). I also purchased the Magoosh subscription and solved 80% of their math problems (with only 75% accuracy).
For Verbal, I did RC section from 5lb Book (~100 questions) and 300 questions from Magoosh (with 57% accuracy).
I, then, spent the third and last week of my preparation using timed practice tests:
Magoosh Estimated Math Score: (158-163)
Magoosh Estimated Verbal Score: (151-156)
Manhattan 1: (156 V, 159 Q)
Manhattan 2: (156 V, 161 Q)
Manhattan 3: (158 V, 163 Q)
Manhattan 4: (155 V, 161 Q)
Manhattan 5: (160 Q) - Skipped Verbal
Manhattan 6: (163 Q) - Skipped Verbal
ETS PowerPrep II: (153 V, 164 Q)
Real GRE: (152 V, 168 Q) = 320
My Quant score was actually higher than any of those gotten during the practice tests. The case is, however, opposite for the verbal side. I studied around 6-8 hours everyday for three weeks (147 hours approx:). Needless to say, 100 of those hours were spent practicing the Quant section because it's not as easy as people seem to believe. I have a really good mathematical background but still GRE has so many tricks in the bag that you can't find your way around without a lot of practice.
In my opinion, Magoosh and Manhattan provide the best test prep material for GRE (after ETS of course). I think they provided me with sufficient material to ace the GRE (Well, atleast the Quant Section). Good Luck