Recommended Frequency

I'm using PWM to control two wheelchair motors (with an H-bridge linking the two). From your experience, what is a good frequency to use? Obviously if it's a ridiculously slow frequency you might feel the effect of stopping and starting all the time, but other than that does it make much difference?

a high one I'm afraid i don't understand, to me it would make more sense to use a high frequency. can you post the schematic?

I believe that if it is too low, you will hear the PWM signal at the motor.
For RC applications, I believe that around 2 KHz is commonly used. For a brushed motor, the "punch" the motor delivers can be modified by changing the PWM frequency.