Yeah, Frostner shines (as the name implies) against any enemy that is vulnerable to frost. Its pure blunt damage is negligible, and its spirit damage so-so. The silver sword is much more preferable if you want to dish out the pain against undead, since it has high slash damage AND higher spirit damage.

Frostner is good against fuling, as they get slowed down considerably. Probably its best applicability, or in swamps, when you have to go back to it for iron.

Against Yagluth I would definitely prefer the silver sword.