Hello Gunjan , There are various branches that you can specialise in for M. Tech. It is a matter of personal choice.

Personally I think that computer designing/ machining is the best branch as it has a lot of scope in the future due to modernisation. You actually create new parts and observe their characteristics using softwares. This is also useful if you are interested in research.

Other than that you can go for automotive engineering, fluid analysis, thermal engineering etc.

I hope this would be useful for you.