Mom, usually, mainly because she was always home and Dad was on the road a lot with work. "Wait until your father gets home" could have meant waiting a few days.
That and they both SWORE that they would never do that because they felt it put Dad in an unfair position to have a good relationship with us.
But Dad still scared the heck out of us! He scared almost every person (male or female - friend or boyfriend) that my sister or I ever brought home. He could give "The Dad Look" without even knowing it, and make people who barely knew him feel about 1" tall!
My best friend in college got her nose pierced not long before I graduated. It didn't bother her to go home and show HER parents, but she was really scared of what MY dad would say, even though she had only met him a couple times.