Nylon.
Pure nickel, IIRC, since it's the softest of the normal string materials...outside of cat gut and nylon.If you figure that stainless steel frets last nearly forever, it would make sense that stainless and other steel strings would be harder on nickle based frets.
There was much faster fret wear under the G string when I started using a wound 3rd on my Epi dot. Even with the plain 3rd though I notice that more fret wear develops beneath the G string than any other string on my guitars.
Lighter gauges, low action, and a lighter touch seem like a safe bet for reduced fret wear . . . simply because you'll be pushing down less firmly into the fretboard every time you fret a note.
There was much faster fret wear under the G string when I started using a wound 3rd on my Epi dot. Even with the plain 3rd though I notice that more fret wear develops beneath the G string than any other string on my guitars.
Lighter gauges, low action, and a lighter touch seem like a safe bet for reduced fret wear . . . simply because you'll be pushing down less firmly into the fretboard every time you fret a note.