Hi! Congrats on your admits and I found your topic in the GMAT sub-forum.
My guess is you have already declined ISB since the cohort started but my suggestion would be to attend the school in the country you plan to work in
If you want a career in India, then ISB
If you want to be in Singapore or you want to have some fun traveling then NUS. I think there are some folks who are able to command a premium with foreign MBA in their home country. That's something for you to answer as I know little about India (sorry) but it may work ... I know some of the folks from IESE and other EU schools are able to find good jobs in home countries that pay a premium. There are some opportunities when companies are looking for westernized staff but they are not many.
At the same time if you are thinking about IB and Finance, makes sense to try to find a job in Singapore - more opportunities perhaps there.