UPSC Mechanical engineering is certainly best as it produces immense job opportunities across sectors like Manufacturing, Metallurgy, Automotive, Defence and Indian Cabinet.

Students are required to appear for  Engineering services  examination viz. ESE.

Students can then join Cabinet posts after years if experience into Raikways and defence.

Also job opportunities offered by CSIR, DRDO, NHPC, Indian Railways.

https://en.m.wikipedia.org/wiki/Indian_Engineering_Services