a mechanics view
Currawong, I will defer to others about the aerodynamics and so forth.
As a Engine fitter and then Dual Trades, I preferred the Porter due to it's simplicity and having Pratt and Whitney power.
The Nomad was more complicated, for instance the system for the flap/aileron/spoiler interconnect was a nightmare.
As mentioned earlier the constant chip lights from the early three planetary geared prop reduction gearboxes was a huge issue.
Structural failure was the cause of Crash Donovan's death, I recall no other structural or aerodynamic failures.
Flying into terrain in Kokoda isn't failure of the machine.