Which B.Tech stream is the best to get into ISRO & NASA?

The core branches like CS, mechanical and electronics are the ones to work at ISRO. Check here for more details http://www.isro.gov.in/careers For NASA, apart from the branches mentioned above, aerospace/aeronautical degree also helps. http://nasajobs.nasa.gov/default.htm

Well, aeronautical engineering, of course at top. Besides, there are several other branches Mechanical Engineering, Aerospace & Communication, Electrical & Electronics, Chemical, Civil Engineering. But, there are very few seats or vacancies for the students of these branches. So, go for Aerospace.

There are many computer, electrical, electronics, mechanical, chemical and mainly aerospace engineers working in NASA.

You should opt for aerospace engineering if you want to work in ISRO or NASA. You should get admission in the IIST for the same.

Of course, aeronautical and aerospace engineering.

aeronautical & aerospace