There are several colleges offering post graduation courses in engineering. Speaking specifically about Mumbai, in my opinion the following colleges offer the best of the faculties,facilities and courses:

1. Indian Institute of Technology-Bombay(Powai)

2. Veer mata Jijabai technological institute(Matunga)

3. Sardar Patel college of engineering(Andheri)

4. KJ Somaiya college of engineering(VIdyavihar)

PS: The above suggestions are not branch specific and these colleges offer master's courses in various subjects. If you are a chemical engineer then i suggest ICT (Institute of Chemical Technology), it is one of the best colleges in India for chemical engineering and PG courses and i highly recommend it.

Good Luck!