Hardeners to use (primary/secondary):
Angels - Explosive/Kinetic
Amarr Navy - EM/Thermal (about equally)
Blood Raiders - EM/Thermal (about equally)
Caldari Navy - Thermal/Kinetic
Gallente Navy - Kinetic/Thermal
Guristas - Kinetic/Thermal
Khanid - Thermal/EM (other damage types often mixed in)
Mercenary - EM/Thermal (Kinetic missiles)
Mordus - Kinetic/Thermal
Odamian - Kinetic/Thermal
Rogue Drones - Exp/Kin with some EM (queens and rulers)
Rogue Pirate - all damage types, no clear focus
Sansha - EM/Thermal
Serpentis - Thermal/Kinetic