Main Damage types to use on npc factions:

Guristas - Kinetic Pithi Pithum Pith
Serpentis - Thermal Coreli Corelum Core
Mordus - Thermal & Kinetic
Blood - EM & Thermal Corpii Corpum Corpus
Sansha - EM & Thermal Centii Centum Centus
Angel - Explosive Gistii Gistum Gist
Mercenary - Thermal
Corpum - EM & Thermal
Gist - Explosive

Amarr: EM or THERM
Caldari: KIN or THERM
Gallente: THERM
Minmatar: THERM

** Damage types enemy shoots **

Guristas - Kinetic(78%) / Thermal (22%)
EoM - Kinetic / Thermal
Serpentis - Thermal(62%)/Kinetic(38%)
Blood Raider - Thermal(48%)/EM(52%)
Sansha's Nation - EM(57%)/Thermal(43%)
Angel Cartel - Kin(26%)/Exp(58%)/Th(11%)/EM(5%)
Minmatar Fleet - Thermal / Explosive
Mordus - Kinetic / Thermal
Corpim - EM / Thermal
Gist & Galente - EM / Kinetic / Thermal
Drones - All