Volume Control - Logarithmic Potentiometer Placement
In general, putting the volume control as late as possible in the signal chain maximises the resultant signal to noise ratio. As the volume is turned down the noise is too. This works well if the system input signal level is always within limits.
In cases where the input signal might exceed the range of the amplifier it would be common to add one at the input to allow attenuation of the incoming signal. Using this as a volume control would result in the unattenuated noise of your circuit being fed to the following stage.
VF3 is the place to put it. Check for DC offset at the output. If there is any you should add a DC blocking capacitor or an offset adjust to eliminate the offset.