Both the colleges are almost similar since they've similar placements as well. So you can choose a college with personal comfort like which ones near to you, travelling, etc. I would've gone with IMU Mumbai since its infrastructure and surroundings environment and locality is pretty attractive and worth enjoying.

Kindly refer to the sites below for more detailed information..

https://www.careers360.com/colleges/indian-maritime-university-mumbai-port-campus

https://www.careers360.com/university/indian-maritime-university-chennai/bsc-nautical-science-course

Best wishes. Thank you.