It completely depends on your interest. Go for the branch you are completely dedicated to.
If you are not channelized to particular branch then refer to the following answer:-
Mechanical is evergreen branch. You can get job in automobile sector, manufacturing sector, production, power, aerospace, petrochemical etc. There are many options even for higher studies. You can get job in PSUs which are dream companies for many mecha folks.
ECE is software branch. You'll be confined to communication, electronics, codings, etc. You may apply for software as well as some core company. With increasing digitalisation one may expect growth in this field.
Choose wisely. Thanks