Choosing a right GMAT institute is always a tough task. Because every institute says they are the best. Isn’t it? What makes it worse is that you will find at least one guy from the institute has scored more than 720. And that makes us confused.
The best way to choose a GMAT coaching institute is to take a mock test with the institutes. Follow this up with a counselling session with an expert in these institutes. What is also important is that you take the review of existing students and if possible some seniors or someone you may know who would have prepared for GMAT before.

1) Make sure you attend atleast 1 demo class. It is not a question of money alone but your precious time. You don’t want to end up spending weeks in a coaching which is not adding value. The faculty should have taken GMAT and should speak sense (which you can figure out after a 3-4 hour class).

2) Ensure that the reasons for joining a GMAT prep course are right. there are 3 reasons for anyone to do it

(a) teach you stuff you cannot learn from a book

(b) ensure you are on the straight and narrow

Source: http://fountainpreps.com/gmat-coaching-centres/