Which has the better faculty in civil engineering, IIT Guwahati or IIT BHU?

Honestly speaking, this internet-controlled era hardly requires good teachers as everything is available on the net. You can get in touch with internationally proclaimed professors with just a click. As far as IIT faculty is concerned, all IITs have similar degree holders that are quality knowledgeable. 

A good teacher is the one that hones your talents to the fullest. They not only help you acquire knowledge but also shape your thinking style. Every institute has a few teachers that influence a student in a unique way. I am sure both IIT Guwahati and IIT BHU will have similar teachers. 

Ultimately, what matters is the environment and the activities that these colleges will provide us to expand our intellect and maximize our talents. Pay little focus on the faculty and look for the right field to enter that will help you shape your career. Personally, I would suggest you go for IIT Guwahati as it has more open-minded and active people in that area which will give you considerable freedom to think and perform.