It all depends on what you are hitting with the ommer and what results you intend to achieve.
My ‘Soft’ faces have a variety of heads, all produced in the workshop, which vay from lead (very soft), thru copper, brass, Delrin, Nylon, etc.
It all depends on what you want your ommer to achieve
A little more info on what you are using the ommer for will assist in advising suitable materiels.
regards
CB