Government Law college and NMIMS Mumbai both are good law colleges in Mumbai.
But GLC Mumbai is definitely better as it is among the top Law colleges in India. It is the oldest Law college in India too. The faculty and opportunities there would be better. Also, GLC Mumbai is a government college hence the fee is also a lot lower. There are good placements in both the colleges but placements opportunities in GLC Mumbai will be better as it is really good reputed and old college. There has bewn a past record of placements from top law firms like AZB, Amarchand Mangaldas etc. Hence if you have a choice between the two, GLC Mumbai would be a better choice among the two.
Best of luck