How should I choose a good Indian institute for Ph.d in mathematics?

I am in my final semester of my Masters in mathematics. I am currently interested in applied mathematics, preferably finite element method(FEM) .

The csir answer key is out, and I am hopeful of getting among the top 20 ranks in CSIR-JRF exam.

How do I choose a good institute in India for doing my Ph.d ? Even if I get a good institute, what is the guarantee that I would get to work in applied maths, under a good professor?