It probably depends on your scoring range, and what your goals are. I think you definitely want to like at OG11 and work all the questions. It should be good enough to get you to a 700 level in math.

If your more ambitious, and have the time, go through the Manhattan GMAT books. Focus on the parts that are challenging to you (combinatorics, ratios, probability, etc.).

What I've found is I know how to work probably 98 out of every 100 questions, but what I notice there are problems that the gmat expects me to get in 2 minutes, that might take me 4-5 minutes. And you simply don't have time for that on the test. It was fine on a paper test because you fly through the easy questions and spend more time on the hard ones. On the real GMAT, you really cant make up for lost time because you keep getting harder questions.

What's the best resource for improving your GMAT mathamatical ability?
>> Standard GMAT books are sufficient to improve your GMAT Math's score.

Right now I've been using McGraw-Hill's GMAT for math.
>> For basic its ok..but don't spend ample time on learning Math's concepts.


>>

• Kaplan, Manhattan, OG 11

Best material for GMAT preparation. Understand questions types and tricks.

>> but since I am short in time I would like to know which one is best.
Official Guide and GMAT prep test are best for you. Don't spend ample time on Kaplan, make your target to complete it than switch to OG.


Regards,
Farooq

What is your target score? Do you consider math a strength of yours?