I will try to answer this query as per my limited knowledge.
As for GMC, its teaching standards have declined. The classes aren’t as rich as in previous times. Even the study culture isn’t as good now. Only the brand name remains. Because of this, GSMC is currently much better ranked than GMC. So if you are from Lucknow, choose KGMU over GMC Mumbai. MBBS is quite stressful, and homely support does a lot for mental health.
Both GSMC and KGMU are good medical colleges. Choosing between these is a bit difficult. Research on the condition of PG reservation at Maharashtra colleges, and Provincial Health Services (PHS) rule in UP. This will help you make a better decision.
Both GSMC Mumbai and KGMU are excellent choices.Choose between the two based on various factors that I have listed above.