which motor will give the most run time?

[molak]

The one that produces the power your need at the higher efficiency..

It´s a complex matter... It depends on how you gear it, the effieciency "curve" of your motor, the efficiency of your ESC and how you drive it.

Batteries are your power source, a limited one, so each time your slipper slips or your wheels spins, you are shortening your run time..

pd: the efficiency curve should be a 3d map rpm, torque and volts.