Hello, aspirant,

Both the branches are important at their own place. It depends solely on your choice whether you would ho for marine engineering or mechanical engineering.
It can be said that it totally depends on how you want to shape your future.
According to the present scenario, for Jon opportunities mechanical is a better branch. It gives you vast opportunities like a job, you can also prepare for UPSC, banking exam, PSU's or rather do M. Tech afterwards.
But if you are sure that you are interested in Merchant navy then go for marine engineering only. Its fees are comparatively greater than mechanical engineering.
But the salaries are also higher. 
I would suggest to try in IIT's and nits for better opportunities.