It's a more intriguing question than you might expect. Training aircraft should IMHO not necessarily be the easiest to fly and I would tend towards aircraft that demand good rudder and speed control.
The three aircraft you mention are pretty docile and can be hacked around the sky and generally re-used after arrival. Of the three, the C172 prefers a little more thinking ahead but none will demand the finesse that many of those on this forum exercise as a matter of routine.