Life at BCG/McKinsey is more difficult. During your B-School years, you will have fewer numbers of distractions like social commitments, attending to family, etc. So, you can easily focus on your studies. The perform or perish culture makes life at BCG/McKinley more nerve-wracking.
These companies pick 2-3% of the top students from the most reputed B-Schools in the country, so competition is way higher.
If you survive the first semester at IIM Ahmedabad then you can survive almost anything. This will give you a pretty decent idea about how tough it is to survive through IIM Ahmedabad. However, let us look at the academics and career at MBB have a stark contrast.
Although, beware of the environment at MBB as it is highly competitive for all people and there is an up or out culture as well. In this case, you might be one of the top ones to be promoted and if luck is not on your side, you will join the rest of the crowd. Such people are asked to look for other career options all while staying in the same designation.
Moreover, the institute also follows a gender diversity policy. This coupled with the type of career progression mentioned above could increase the competition even more among males. But, if you are an IIM Ahmedabad graduate, even if you are not promoted, you will still have good exit options to choose from.
A friend of mine also experienced a similar thing. BCG MCK BAIN is known to promote the hiring of female employees through their woman-based quota as this is standard American practice. Women should make up at least one-third or one-half of the total employees. If you are in the US, then one-third of those employees should be international.
A classic case is one between two of my friends. The female was an IIM Ahmedabad graduate and she did not have any IT experience and still became the VP at Infosys within 8 years. Whereas, a male friend who graduated from the same place in PWC is an AVP after 15 years.
In my opinion, IIM Ahmedabad will toughen you up with its academic rigor for your future and ultimately, it is up to you as to how you want to apply this knowledge.