There are 10 different types of Anomaly Class - Class 1 (easiest) to Class 10 (hardest).
Class 1 = (Faction) Hideaway or Drone Cluster (easiest)
Class 2 = (Faction) Burrow or Drone Collection
Class 3 = (Faction) Refuge or Drone Assembly
Class 4 = (Faction) Den or Drone Gathering
Class 5 = (Faction) Yard or Drone Surveillance
Class 6 = (Faction) Rally Point or Drone Menagerie
Class 7 = (Faction) Port or Drone Herd
Class 8 = (Faction) Hub or Drone Squad
Class 9 = (Faction) Haven or Drone Patrol
Class 10 = (Faction) Sanctum or Drone Horde (hardest)

Each Anomaly Class has 4 different level's
Level 1 = (Faction name) + Anomaly Class (easiest)
Level 2 = (Faction name) Hidden + Anomaly Class
Level 3 = (Faction name) Forsaken + Anomaly Class
Level 4 = (Faction name) Forlorn + Anomaly Class (hardest)
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Resistance to use

Guristas - Kinetic / Thermal
Serpentis - Thermal / Kinetic
Blood Raider - Thermal / EM
Sansha's Nation - EM / Thermal
Angel Cartel - Kinetic / Explosive / Thermal
Minmatar Fleet - Thermal / Explosive
Amarr Navy - EM / Thermal
Caldari Navy - Kinetic / Thermal
Gallente - Kinetic / Thermal
Mercenary - EM / Thermal / Kinetic
Mordu's Legion - Kin/Thermal
Drones - EM / Thermal
Khanid - EM / Thermal
Thukker - Explosive
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Best Damage to NPCs

Guristas - Kinetic
Serpentis - Thermal
Mordus - Thermal & Kinetic
Blood - EM & Thermal
Sansha - Thermal
Angel - Explosive
Mercenary - Thermal
Arch Angels - Kinetic/Thermal