CAT

I am especially qualified to answer this question as I have attended the classroom program of both TIME and IMS. I will be comparing the classes on different parameters.
1.) Study material
Time has a vast number of questions especially for quants. The questions though were quite repetitive. For each specific type of question, there are atleast 2 more which would be almost identical but with different numbers. This is good for people feel comfortable solving more questions of the same type to get the hang of it. It also has a lot of passages for Reading Comprehension and exercises for measuring and improving reading speed.
On the other hand IMS follows a different approach. They have lesser number of questions but most of them would be unique. I personally found this better because you get a sense of completion on finishing the chapter wise exercises and also have more time to go over questions from other sources.
The place where IMS steals the show is the materials for English. The passages are top notch and of a really good level. The solutions too are better explained. Most of the students who have studied from different materials feel the same about the IMS English material.
2.) Classroom environment
The batch that I had joined in TIME was really crowded. The faculty were good but kept changing and I didn't get time to properly interact and bond with a specific set of faculty. This was my personal experience and could have been different for others. Moreover I was in the third year of my engineering and wasn't so serious about CAT and that could have had an effect over my experience.
In the case of IMS, I had joined the Vashi branch. The batch size was undeniably lower and the faculty I had was really good and took personal interest in your preparation. This really helped me keep up the motivation and also helped me improve on a weekly basis.
3.) Test-Series
Both the classes offer a really good set of mock tests. The analysis provided is also comparable and they keep making improvements to their Test Series modules. So nothing much to differentiate here.
So overall from my personal experiences I would recommend IMS over TIME.