It depends on what you are playing but generally Thorns for melee, archers of all kinds, ghosts, souls, dolls, beefcakes like minotaurs. See this poll https://forums.d2jsp.org/topic.php?t=108799698&f=148

Snake and Defiler Warriors (same as Pindleskin) because of the Charge, combine that with ultra high ping and death is upon you.
Bone archers are a pain in the ass aswell, especially since merc will die super fast cuz he can't leech.

As a javazon… high hp ones with thorns and light immunity