reftex-vref-is-default

reftex-vref-is-default is a variable defined in `reftex-vars.el'.
Its value is

nil

• This variable is safe as a file local variable if its value
  satisfies the predicate `(lambda (x) (or (stringp x) (symbolp x)))'.

Documentation:
Non-nil means, the varioref reference style is used as default.
The value of this variable determines the default which is active
when entering the selection process. Instead of nil or t, this
may also be a string of type letters indicating the label types
for which it should be true.

This variable is obsolete, use `reftex-ref-style-default-list'
instead.

You can customize this variable.