I think it's personal taste. I have a Martin that I tried various pins in, from the original plastic to bone, to ebony to Tusq. I decided I liked the Tusq better. The difference between one pin to the other was small, but certain things about the treble notes just seemed better to me with the Tusq. Maybe they just fit better.
No, I didn't change strings each time, but loosened the strings enough to refit different pins. I did this over 2 days. Yes, I played the guitar in the same room every time to hear it as closely as possible to being under certain conditions.
That's about as scientific as I get, shy of asking for the salt and pepper at the table.
The biggest difference I think I ever heard from a set of bridge pins has to be with my Taylor Baby. I had a set of basswood pins and stuck them in it. I swear, that guitar seemed to mellow out and sound more like a full size guitar with those pins in it.
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