Well. I would have to say the most disturbin' are the sexual sadists. They don't kill to kill. They get off on inflictin' pain, almost always to women. The death is accidental or because he's done with her or necessary not to get caught. Then he moves onto the next one. They are usually long distance truck drivers.
Most serial killa's do a lot of driving too. Stalking, looking for secluded places to dump bodies, etc. Typical pretador behavior.