Which is the best academy to take cat coaching in India, both online and offline...

You can join either TIME or Carrer Launcher. Both of them are equally good in terms of faculty and study materials. IMS is also pretty good and comes right after these two. All of them have good success rate. All of them usually charge above 40000 as the course fee.

But if you don't want to invest such a huge amount of money you can study from various books available in market like Arun Sharma and Sarvesh Verma for quantitative aptitude and magazines like The Economist and TIME and TOI newspaper for the English portion. Along with that do buy the mock test series from the above Institutes which will give you a good knowledge of all the kinds of questions generally asked in CAT,XAT or other exams.

All the very best