Perhaps we should take the sting out of discussion. Personally, I think the following attributes are essential for a PPL training aircraft:
Balanced controls
The ability to clearly demonstrate the primary and secondary effects of all controls (including power/throttle).
An aircraft that rewards use of rudder
Relatively benign behaviour when executing a go-around (not totally benign, just something that allows the student to learn)
Predictable stall characteristics, demonstrating all the attributes that one could expect including buffet and wing drop.
Forgiving in the landing, notably aversion to PIOs and excessive bounces.
FUN! Something that doesn't intimidate the student.