Use your shotgun when facing them at close range, but be careful as they will do lots of damage. You should have a large amount of health and armor if attempting close combat. A few Tesla grenades and the Assault Rifle will work well at medium range. To take them out at long range, use the Marksman Rifle or Laser.

Under the Uber difficulty setting, try firing constant shots from the AR Marksman's automatic plasma rifle. A few shots fired using the LaserKraftwerk's Targeting Scope at close range also will kill them. Getting two direct hits with the Rocket Launcher will also take one down.