Enemies ------- Hardener to use ---------- Damage type to use

Blood Raider --- EM/Thermal --------------- EM
Guristas ------- Kinetic/Thermal ------------ Kinetic (Vespa)
Sanshas ------- EM/Thermal --------------- EM
Serpentis ------ Thermal/Kinetic ------------ Kinetic
Angel. --------- All Resist (Explo/Kin) ------ Explosive
Mordus -------- Kinetic/Thermal ------------ Kinetic
Rogue Drones -- All Resist (Explo/Kin) ------ EM
Mercenary ----- All Resist (EM, Therm) ----- Thermal
Minmatar. ------ All Resist ---------------- Thermal, Explo
Gallente. ------- Kinetic/Thermal (sec. EM) -- Thermal
Amarr --------- EM/Thermal. -------------- Thermal
Caldari -------- Kinetic/Thermal ------------ Kinetic

http://games.chruker.dk/eve_online/damage_types.php

http://theelitist.github.io/eve-drone-rat-damage-types/