hello aspirant,well ,both are really good ,but it all depends on your perception and your grasping nature.if you are really having that much high grasping power and fast and efficient understanding of topic then its better to go for online coaching,  and it depends on the way you follow. if you are little bit weak in grasping concepts, you better go for a coaching centre and there you will get to know what is the reality inside that concept.since, both are good ways to prepare,  but you need to have a note of each and everything you study and it will helpful for future purpose.here i will suggest you some of the   coaching centres for CAT preparation:" T.I.M.Ecareer launcher.bull's eye. hope you understood ,thank you