the best training plane is one that is comfortable to student and instructor and allow large people an uncramped environment.
it should allow for both student and instructor equal access to all critical controls
it should allow excellent visibility to allow for visual clearing and vigilance in avoiding other planes/traffic
It should be robust and reliable and of pleasant, not unusual handling qualities. It should be of sufficient range and reserves to allow for long cross country requirements in obtaining both private and commercial licenses. It should also be a good instrument platform for obtaining INSTRUMENT RATING.
IT should have heated pitot and be capable of handling a lightning strike.
FOR practical purposes, I would think that the piper cherokee series is about right.
There is plenty of time to allow a student to go hunting for odd planes, tail draggers, biplanes, eaglerocks after the gentle introduction to the world of the air.