RE: Which plane would an instructor fear the most?
There's a world of difference between a Decathlon and a Citabria wing. The Decathlon has a symmetrical airfoil and little if any dihedral and for some reason some versions of the Decathlon models are bad about dropping a wing on final approach. But the fuselages are very much alike.
A Citabria should fly almost like a Cub or maybe even better
I never had any trouble with a Cub but I've sure seen guys at the field have a lot of trouble keeping them straight on the ground.