Hi Akanksha.
Your best move may be to take a practice test before choosing prep resources so that, when you choose resources, you'll have the benefit of knowing your current level and thus what you'll have to accomplish to achieve your target score.
The best test to use for this purpose is one of the free official practice tests on mba.com, which fairly accurately represent the actual GMAT.
Before you take the test, you should prepare some to familiarize yourself with the GMAT and its question types so that you can an accurate score, as opposed to one that's low just because you lack familiarity with the test.
Once you have that score, you'll be in a better position to decide which resources you'll need and how long you'll likely need to achieve your target score, and you could add
Target Test Prep to your list of options. Also, you can try each course by signing up a for a trial.
For some more tips on how to prepare for the GMAT, see this post.
How to Score 705+ on the GMAT Focus Edition