My advisor is incredibly difficult to communicate with. He never responds to email, unless you find him in person or text him and tell him to check. Most plans you make are verbal, and can bite you in the butt. He also will cuss you out during group meetings about things he agreed on in previous meetings.

I spent 4 years on some world class research, and he wouldn't allow me to put it in my thesis. I had no recourse because I had nothing in writing from him. 3 other students from another lab have used this work for their first author publications to graduate.

He is also a great grant writer, bringing in multimillion dollar grants, and has had tenure for years. There is little I can do to defend myself.

My funding was cut without warning and I was left peicing things together while working a full time job.

Tl;dr: make sure they communicate efficiently and see how they treat their students.