Thermal is almost always second best type to deal.
Faction - Damage Type to Tank For - Damage Type to Deal
Angel Cartel - Kinetic/Explosive/Thermal - Explosive
Blood Raiders - EM/Thermal - EM
Guristas - Kinetic/Thermal - Kinetic
Mordu's - Kinetic/Thermal - Kinetic
Sansha's - EM/Thermal - EM
Serpentis - Thermal/Kinetic - Kinetic
Amarr - EM/Thermal - EM
Caldari - Kinetic/Thermal - Kinetic
Gallente - Kinetic/Thermal - Kinetic
Minmatar - Explosive/Kinetic - Explosive
Khanid - EM/Thermal - EM
Mercenary - Kinetic/Thermal/Explosive/EM - Kinetic