Gear reduction vs PWM duty cycle limiting

Hello, I am wondering about adjusting the output RPMs of wheels. Lets assume two situations.

  1. We have got gear reduction, that reduces motor RPMs to Wheel RPMs that causes required maximum velocity for maximum possible PWM duty cycle.
  2. We do not reduce motor RPMs too much, instead we limit our PWM duty cycle to value, that causes required velocity.

What are the pros and cons of that variants? What should I apply? (In first situation there may be a problem with too much gear reduction required - hard to apply it in the mechanical meaning).