I have both ebony and brass pins that fit my Guild F-30. I swapped them back and forth each time I changed strings for several cycles one year. That last time this debate came up in fact. I found not difference in the the sound from each change. Once I played them with the pins alternated and found no difference in the tone.

There is a perceptible difference between plastic pins and pins of a denser mass. But on that guitar with my ears there is no difference in the brass and ebony pins.

D