Damage types

Enemies ------ Hardener to use -------- Damage type to use
Amarr --------- EM/Thermal. -------------- Thermal
Angel --------- All Resist (Explo/Kin) ------ Explosive *
Blood Raider --- EM/Thermal --------------- EM
Caldari -------- Kinetic/Thermal ------------ Kinetic
Gallente ------- Kinetic/Thermal (sec. EM) -- Thermal
Guristas/Pith --- Kinetic/Thermal (sent. EM) -- Kinetic
Khanid -------- EM/Therm/..? ------------- EM / Thermal
Mercenary ----- All Resist (EM, Therm) ----- Thermal
Minmatar ------ All Resist ---------------- Thermal, Explo
Mordus -------- Kinetic/Thermal (EM?) ------ Kinetic
Rogue Drones -- All Resist (Explo/Kin) ------ EM
Rogue Miners -- EM/Explo (all?) -------------EM
Sanshas ------- EM/Thermal --------------- EM
Serpentis ------ Thermal/Kinetic ------------ Kinetic

http://games.chruker.dk/eve_online/damage_types.php
http://wiki.eveuniversity.org/NPC_Damage_Types