In uk.d-i-y handy-andy wrote:
What is best for testing moisture content of wood, a two pin or a four pin
tester?

Four pin will give more comparable results.
Two pin is much more dependant on probe condition, and contact with the
wood, four pin - ideally - should not depend on this.

A sharp plug cutter, an oven at 100C for an hour, and a sensitive scale
is of course the best way.