GMC Mumbai and GSMC have always been compared to each other.
GSMC has great academics and a very competitive environment. GMC is much more relaxed. At GMC, you’ll come across a variety of students- from nerds to all-rounders, to those who study the night before an exam.
Toppers generally choose GSMC as their first preference. But those who spend some time in Grant, usually refuse to be upgraded to GSMC. Grant students are better at extracurriculars, while GSMC students are on average, more studious.
Both are good for an MBBS degree. You should choose between them based on your personal preference.