Hi PrijitDebnath,
Since it sounds like you're in a 'research' phase, you've come to a great source for information. When considering the various ways that you can prepare for the GMAT, you'll really want to investigate the options thoroughly. Most GMAT Companies offer some type of free materials (practice problems, Trial Accounts, videos, etc.) that you can use to 'test out' a product before you buy it. We have a variety of those resources at out site (
www.empowergmat.com). I suggest that you take advantage of all of them, then choose the one(s) that best match your personality, timeline and budget.
As far as your overall timeline is concerned:
1) When are you planning to take the GMAT?
2) When are you planning to apply to Business School?
3) Do you know which Schools you plan to apply to?
GMAT assassins aren't born, they're made,
Rich