Damage to tank:
Guristas ------------------Kinetic / Thermal
Serpentis ----------------Thermal / Kinetic
Mordu's Legion -------Thermal / Kinetic / EM
Blood Raider -----------Thermal / EM
Sansha's Nation ------EM / Thermal
Angel Cartel ------------Explosive / Kinetic / Thermal
Mercenary ---------------ALL
Rogue Drones --------EM
Amarr Navy --------------EM / Thermal
Caldari State ----------- Kinetic / Thermal
Gallente Navy ----------Thermal / Kinetic
Minmatar Fleet --------ALL (varies)
EOM -------------------------Kinetic, Thermal

Best damage to deal against NPCs
Guristas - Kinetic
Serpentis - Kinetic
Mordu's Legion - Thermal / Kinetic
Blood Raider - EM
Sansha's Nation - EM
Angel Cartel - Explosive
Mercenary - Thermal
Rogue Drones - EM
Amarr Navy - Thermal
Caldari State - Kinetic
Gallente Navy - Thermal
Minmatar Fleet (thukkers) - Thermal