i wanna to be an astronaut,which will be best?b.tech in aeronautics or engineering?

You can not become astronaut as an Indian as NASA allows only USA citizens. There are some joint space programs where other country's citizens are allowed but as of now there is no such program is under consideration from India. After about 10 years India expects to send her own astronauts in the space but they will be form air Force, HAL, ISRO or DRDO. and that person needs to be a Pilot or scientist.
Therefore, you pursue engineering degree in Electronics, Mechanical, Electrical or Computer science. During final year apply for aeronautical engineer's post in Air Force, if selected, your dream in some portion can be fulfilled.

You can not become astronaut as an Indian as NASA allows only USA citizens. There are some joint space programs where other country's citizens are allowed but as of now there is no such program is under consideration from India. After about 10 years India expects to send her own astronauts in the space but they will be form air Force, HAL, ISRO or DRDO. and that person needs to be a Pilot or scientist.
Therefore, you pursue engineering degree in Electronics, Mechanical, Electrical or Computer science. During final year apply for aeronautical engineer's post in Air Force, if selected, your dream in some portion can be fulfilled.