Delhi

Hi Siddharth,
While ISB may have an international standards like campus, it is still a notch lower in pedigree as compared to FMS. Also ISB has a very large batch size as compared to FMS which makes it easier for you to bag coveted jobs at FMS.
You have already pointed out that chasm of difference in the fees of these two B-Schools, also sonce you are in your graudation right now, you will be required to work for at least 2 yearw before even being considered for ISB. That's about the same time you will graduate from FMS considering you get into both of these B schools in the first go.
So effectively, 3 years after your graduation the two scenarios will be:
1) Graduated from FMS with 1 year of post MBA experience and equivalent financial earnings with no debt.
2) Graduated from ISB with no post MBA work experience, most of the 35 lakh debt still in tact even after spending all your 2 yearsafter graduation work experience savings
Also, freshers at FMS are much better off at FMS compared to 2 year work experience students at ISB since the avg work experience is much higher at ISB (5 years at ISB vs ~ 1 year at FMS) thereby putting you at a substantial disadvantage.
On monetary terms, the 2 lakh higher avg package you get at ISB will form a miniscule of the 30+ lakh additional debt at ISB.
Since you are from Delhi, FMS Delhi should by default be a far more preferred option.
P.S. I am from Hyderabad with 1 year work experience, I find FMS Delhi to be a default choice over ISB on all grounds except for the higher standards of infrastructure at ISB.