Jayhawk is right, Sniper Rifle is best...if you can pull it off. Just note that Caretakers are resistant (50%, aka half damage).
Another option is oil spitter and rocket hammer (200%, aka double fire damage when oily), because each "hit" adds to their aggression count, but oil doesn't do damage and therefore doesn't count...however, a lot of them (Caretaker, Alpha, Little Billy Goat, Big Billy Goat) are a little bit resistant to fire (75%), and Bucktooth is normal resistant (50%).
Lightning actually does the most damage to them, because none are resistant and several are actually a little bit vulnerable to it (125%). However, lightning works best overlapping (200% if shocked, 150% if wet, so 300% damage if both), meaning a team of 2-3 all wielding Tesla Hammers and at least one with a Water Rifle can tear through most enemies. Caretakers (75%) and Alphas (50%) are resistant to water, so you could just skip straight to the lightning damage for them. However, this strategy means a lot of "hits" which gets them angry, so you have to finish them quickly, and if you are solo-fighting (or already consistent at getting criticals) it would be better to practice with the Sniper Rifle.