Which field should I put more focus in among propulsion, aerodynamics, structures and avionics while pursuing aerospace engineering?

Hello Hardeep, I feel it's avionics without any doubt. Of course propulsion too has potential but avionics is the field where research is going on in full swing.

If you wand to do R&D Aerodynamics and Structural is best option, for Job prospective Avionics is best.