Hello
DUGGARAJU ABHINAY , For joining ISRO by giving ISRO exam for Scientist/Engineer ‘SC’. The exam is conducted for the Mechanical, Electronics and Computer Sciences departments, out of these this year there were 42 seats in Electronics, 36 in Mechanical and 9 in Computer Sciences.

So, from any of branch ECE or CSE both are best for ISRO.

Hope it will be helpful for you :)