RE: Which plane would an instructor fear the most?
The Citabria I have tends to display some good habits, but using the rudder helps quite a bit. I have not experienced any stalls, but others at the field attributed that to my flying experience and skills. I doubt if I would have the ability to judge how well a new pilot can handle it. I do know that it seems to handle like a Cub, and the instructors at my field recommend the Piper as a third plane at best. They even went as far as saying that a Cessna is closer to being a trainer because of the tricycle gear and longer tail movement. I got bit by one of those once on a steep takeoff, and that's when I learned something about elevator control and how to get the most out of a crashed fuselage. It never quite flew the same.
As an intermediate or second plane, Cubs tend to be the most controversial. People either love them, or hate them. I find them easy, while some others I'm sure find them to be difficult.
NorfolkSouthern