IIM

IIMs and IITs are really focused colleges and can't be compared to the US and European universities. Those universities house various departments which all come together to enrich the student experience. And, additionally due to the smaller size of the universities in India, they have low number of foreign students and faculty. Also, the research output is lesser than universities worldwide due to the focus on placements. But, in general the kind of students that enter and the faculty that teach are the smartest and most hardworking in the world. Also, both the institutions have good penetration in the network, and the students and research benefits from it.
The ranks are for the one year MBA program of IIMs, and don't represent the quality of their flagship PGP Course. Hence, I would say these rankings are not a good metric of assessing/comparing the quality of IIMs against other institutions.

There are a lot of good private colleges which make it to the top brand of B-Schools. The below-mentioned colleges are at the top because of their living experience, placement performance, Selection process, future orientation, alumni networks, brand value, curriculum and quality of education.
1. MDI Gurgaon,
2. SP Jain Mumbai,
3. Narsee Monje Institute of Management Studies Mumbai,
4. Faculty of Management Studies, New Delhi,
5. Indian Institute of Foreign Trade New Delhi,
6. ISB Hyderabad,
7. IMI New Delhi,
8. IMT Ghaziabad,
9. National Institute of Industrial Engineering Mumbai,
10. Jamnalal Bajaj Institute of Management Studies,
11. Symbiosis,
12. Great Lakes,
13. BIMTECH,
14. Goa Institute of Management,
15. Indian Institute o technology Kharagpur,
16. Indian Institute o technology Mumbai,
17. IRMA,
18. TAPMI.
Students can get into these premier institutes by cracking various MBA entrance exams.

We can't say IIM-Ahmedabad is charging very much, but among the IIMs it is on a bit higher side. The facilities provided at IIM-A are really good as compared to any other college. IIM-A has world-class infrastructure in terms of classrooms, dormitories, computer centre, library and sports facilities. The world-class infrastructure created on the institute's hundred-acre campus provides an ambience conducive to stimulating learning. The architecture, classrooms, library, research centres and computing facilities all combine to provide a holistic learning environment.
A state-of-the-art computer network with more than 2000 nodes connects all the members of the institute's community with each other. This network has a fibre optics backbone with one or more fibre segments reaching every building at the campus.
A good library, all sports facilities, and good campus life is what IIM-A offers.

As per my experience I don't think that an year gap affects for CAT preparation adversely affects your chances of getting admission in any institute in IIMs or any other institute of India. The entire interview process is meant to gauge the students on their knowledge, skills and attitudes as well as their inclination of doing a MBA program.
If you are dropping out of your current job for one year there should be a justification as to what were the reason for opting out of your job. There are various examples of students who have scored a hundred percentile while working and thus the interviewers always discuss the reasons for dropping out. But, if you are able to justify it well and convince them about yourself. I personally don't think that it would negatively affect your chances into IIMs or any other institute of India.

At any B school, there is so much to do but you don't have the time for everything. It is very important to know your priorities. And this need not be same for everyone. For some sports is important, some like to read etc. While you have to ensure you spend time on academics every day it is also important you pursue your interests. Prior preparation for classes, attending classes regularly, listening attentively helps to save a lot of time during exams, quizzes etc. Do not try to procrastinate works which will end up burdening you in the end. Do not get influenced by what your friends are doing because they might have different priorities than you. Also, make sure you take some time to spend on your hobbies etc which will act as stress busters. Engage in activities which genuinely interest you. This way you are not tired working. And try to get enough sleep so that your mind is fresh in the class.