One big difference in slate and glass is ease of conditioning. Just a few swipes with a Scotchbrite pad and you are good to go. Whereas with glass/crystal, its going to take a few more passes and I generally use 150 grit sandpaper for that. Copper I use the green Scotchbrite and that is the only surface that when I condition it, I actually swirl the pad around on the call. All other surfaces I push the sandpaper/Scotchbrite in ONE direction only.
I like padauk and jatoba on copper as far as woods. But if you get a chance, get with carp on here and get one of his goose wingbone strikers. That thing flat runs on every surface you can imagine