Is it mandatory to appear for TOEFL or IELTS after GMAT for admissions abroad? If yes then which one is more accepted or preferable?
Yes, It is mandatory to clear either of it.
It is really difficult to say which one is particularly more accepted or preferable. Reason being, most of the universities, every time you check the entry requirements. You will find that they ask for either TOEFL or IELTS.
There was a time when TOEFL was more preferred by US varsities, while IELTS was given more priority in Europe and Australia. Now gone are those days where they prioritised specific exams.