The four types available are Gravimetric, Magnetometric, RADAR and LADAR. A Gravimetric Quest Probe will have 250 points of gravimetric sensor strength and 50 points each of Magnetometric, RADAR and LADAR.

Magnetometric - this is to find professional sites (archaeology and salvaging sites).
Gravimetric - this is to find asteroid belt sites.
Radar - this is to find hacking sites.
Ladar - this is to find gas cloud-related sites
Unknown - this has a chance to find a complex with a chance to escalate.

*** NPC damage types ***

Guristas - Kinetic & Thermal
Serpentis - Kinetic & Thermal
Mordus - Kinetic & Thermal
Blood - EM & Thermal
Sansha - EM & Thermal
Angel - Kinetic & Explosive
Mercenary - Kinetic, EM, Thermal & Explosive
Rogue Drones - Kinetic, EM, Thermal & Explosive

*** Best damage types to NPC ***
Guristas - Kinetic
Serpentis - Kinetic
EoM - Kinetic
Blood Raiders - EM & The