Without a silencer (aka noise suppressor), none. Some may be worse than others, but all will cause hearing damage from .380 on up.
Worrying about hearing damage is the least of your worries. However, if you go that route, get a suppressor or get electronic hearing protection.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011