The following rat types and damage types detail what you should be aiming for:

Guristas: Kinetic then thermal damage.

Blood Raider: EM then thermal damage.

Sanshas Nation: EM then thermal damage.

Serpentis: Kinetic then thermal damage.

Angel Cartel: Explosive then Kinetic damage.



Enemies - Hardener to use - Damage type to use
Blood Raider - EM/Thermal - EM
Guristas - Kinetic/Thermal - Kinetic
Sanshas - EM/Thermal - EM
Serpentis - Thermal/Kinetic - Kinetic
Angel. - All Resis (pri. Expl. ,Kin.) - Explosive
Mordus - Kinetic/Thermal - Kinetic
Rogue Drones - All Resis (pri. Expl. kin) - EM
Mercenary - All Resis (pri. EM, Therm) - Thermal