Hello Koustav Biswas !

Both of them are quite good as far as quality of education is concerned. You can choose Mumbai if you are comfortable living away from home. Few advantages ( I may be wrong) of GMC Mumbai are-

1. The amount of clinical exposure is very high as it is situated in the heart of the city.
2. There is no strictness as such for attendance hence it solely depends on your interest for the subject.
3. It has got some of the best faculty in the country who eagerly wait to clear doubts.(But they have to be approached by the student)
4. The campus is huge and beautiful despite being in Mumbai where space crunch is very eminent.
5. Various professionals visit from all over the world hence exposure to new innovations in medical field is quite good.
6. They have their own gymkhana right opposite to the famous Marine lines hence you won't have problem telling your date out after a workout.(just kidding)
7. Last but not the least,Mumbai is a city you will fall in love with from the moment you come.

Feel free to ask further.