The astrophysics department at IISc is very small and consists of only six faculty and 10–15 PhD students. However, IIA is a major astrophysics institute of India, with several world class facilities (see - Indian Institute of Astrophysics). In IISc all faculty work in theoretical aspects (mostly high energy astrophysics) of astronomy, so you don’t have much choice. Also one important drawback at IISc at present is that, two of the most senior faculty are going to retire in a year or so and they don’t take any student. Other faculties are also very much occupied. This is the reason that IISc is part of JAAP program where you will have opportunity to work with faculties of IIA, RRI, ISRO and IISc at your interest.

Now coming to IIA, there are about 50–60 faculty so obviously a very large group. They work on several topics in astronomy (but mostly stellar or solar physics). Most of the faculty work in observational astronomy as they have their own observatories. IIA is also a very active member of ASTROSAT, therefore you are always in priority of data acquisition (IISc will not be able to get data that easily!). Since they are a big group, they take more people for PhD hence you have higher probability getting there. Only drawback is that, the faculties are restricted to take a certain number of students (and this limit is actually very small) so sometimes even though student and professor have a mutual understanding, student cannot join that faculty. Otherwise, it is one of the best institutes to join to pursue a good career in astronomy.

Hope you find it helpful

let me know in the comment box if you are having any further doubts

thanks

Good Luck!

Related to package astronomy is not good overally but you should have interest inorder to go higher in it,it is generally difficult to go to higher in this branch but if you have interest you can go to peak stage becoming insane in it.So, well it is up to you and it depends on you usually.