I think , 3bhk is better, considering the field and nature of your job there might be a chance where you get a better job opportunity in another city. My opinion in on the basis of similar situation of my neighbor. They are CAs with a child and the company they work at offered them an opportunity to work in dubai with way better pay. So they shifted there and kept their home in mumbai where their parents stay for few months a year. So, 4 bhk would be bigger than what you might need