My shotgun range rod is hedge; one of a baker's dozen I made in '81. The problem was finding a 48" piece of straight-grained hedge to split them out of. It is black with age and fouling, and has loaded most of my 20 gauge and larger range loads since it was made. I've seen a hedge ramrod on an original rifle marked ".H. E. DIMICK St. Louis", but that thing is almost .70 caliber.
White ash works for a ramrod, but tends to split when used with a tight patch-ball combination (works great for a shotgun). Black ash splits along the grain lines when flexed; I had one last a summer but it was fraying by August. I had an M. Fordney rifle that came with a white ash ramrod, but have no idea how old it was.
Split walnut and white oak work OK for a shotgun, or maybe a range rod for a larger-bored rifle. When worked down to fit a rifle they break easier than hickory.
Greenheart and purpleheart make great pistol ramrods but I've not tried making longer rods from either.