During my initial days at IIT Patna, a professor once said that most of the professors there were good. “Most?” I asked immediately. To which he responded that all of them are good at research but some of them are terrible teachers.
A professor at IIT acknowledging that there are bad teachers in such a prestigious institute which I dreamt of was really shocking for me but now I am used to it.
So to answer your question, if you are asking about qualifications, all of them are good.
But the truth is that all of them are good researchers in their fields but not all of them are good teachers.
You will find professors whose classes you will love to attend and won’t even mind attending an extra class. But, at the same time, you will find classes when you would be watching outside the window thinking that outside world is amazingly beautiful. You will have to teach yourself a subject because your professor was terrible at teaching.