Instead of institutes, you should compare programs. Assuming that you are comparing the ISB full-time program (PGP) with the IIM one-year full-time program, IIMA PGPX, here are some of the things that you should consider.
IIMA PGPX has its own advantages, but ISB PGP stands out due to the above reasons.
This question definitely does not have a straightforward answer. You will have to look at a number of parameters in order to reach a conclusion. In my opinion, you should not compare the placements between either institute as those are quite subjective. It is suggested to check the website of each institute.
Admission:
Aim of the program:
Batch size: IIM admits about 80 students per batch and ISB admits about 800. Depending on your requirement, this could be a pro or con.
Other plus points at both colleges include the fact that they both have a good brand name. Plus, you might not need an industry internship if you are an experienced professional. Although there are few companies that visit the colleges, they hire a larger number of people. There are a number of other pros that you will experience once you decide to go to either of these places.
You will definitely have a good future at either of these places.