Dave,
That's easy: you need both! Since the application is aerospace propulsion i was making the assumption that the motor/gen would already be geared to run at as high RPM as practical. Having got the most power for a given torque, the ideal design then seeks to reduce the mass for that torque. This is accomplished by minimising NdFeB magnetic circuit length, which is the objective of disk motors.
To get partly up to speed check out
www.uqm.com
I have read about higher performance developments for various applications, but couldn't find any of the ones i was thinking of in my quick google session...
For a rotor hub application you would still need to gear the motor down, requiring a serious epicyclic reduction gearbox. In a tiltrotor this drivetrain rotates into the airflow, in an interleaving heli the drivetrain would likely present a serious drag element. Notice i still state that a mechanical drivetrain would be required in the tiltrotor. Your application was also to try to remove the mechanical drivetrain, which i still believe to be impractical.
Mart