I look for hardness 1st then the tightness of the end grain for strikers.
The call can be just about anything, it's what is placed on them that make the sound, but its the striker and quality of the wood that actually plays the music.
Being a furniture restorer I've seen just about every wood used for making furniture , instruments exc. So knowing the quility of wood comes easy. What I'm having to learn are technical aspects of tuning wood. I'm in the process of making a wood stabilizer box to stabilize more open grain woods like the maple burl , spalted wood which was created by water seeping into the wood degrading it, so it needs to be stabilized (hardened)
Here is a beautiful African Blackwood {Ebony} striker. Pulling on the grain in Ebony takes a bit of sanding but once out and finished it looks great but sounds even better , $35.00 shipping included.
Here is the African blackwood finished, Couple of strikers, Burzilian rosewood and African Blackwood
Turned to a high polish. The way the African looks polished up is anything but black and the rosewood has beautiful figure.