What is the proper configuration for an adjustable voltage divider circuit
The right one is the best for a number of reasons, the left version is very rarely used:

1: The right one can be adjusted linearly from 0-100%  (assuming a linear law potentiometer). Or it use a logarithmic law potentiometer that is preferred for audio applications.

2: The left one depends upon the actual resistance of the variable resistor that is usually not very well controlled (maybe 10-20%). The right one does not depend upon the absolute value.

3: The left one cannot be adjusted to give zero output. The minimum is when RV2 is at its maximum value, but the output will not be zero.

4: The left one puts a significant current through the wiper of the variable resistor. Because of contact resistance variations as it is adjusted this can cause noise in the output. It is not at all suitable for audio value control.