As some of my friends studied at IIT Ropar, and also after reading some reviews online, I can say that the best professor is Dr. Dhiraj K. Mahajan. 

He values knowledge above marks and he takes his own open time exam for students to understand their potential.

He has guided 5-6 students personally for a year and with his efforts. He helped students in securing a job opportunity in Germany for international exposure. 

Apart from him, here are some of the other good professors - Dr. Narayanan C. Krishnan, Dr. Nitin Auluck, Dr. Balwinder Sodhi, Dr. Deepti Bathula, Dr. Apoorva Mudgal, Dr. Yashveer Singh, and Dr. M. Prabhakar.