The Ray gun or the Thunder gun. ( However it also depends on the map, like in Call of the Dead instead of the Thunder gun its the VR-11, for the map Five it's the Winters Howl.) Hope this helps.
Ray Gun
ak74u
Ray Gun and also the Thunder gun, when upgraded, it's a beast combo when you are overwhelmed
M14
Pray really...
Porters x2 ray gun and zuse cannon
The random box.
it has to be the wunderwaffe dg-2, its one hit kill forever and it connects to zombies with electricity
The Ray Gun is only available in the Nazi Zombies mode and can be obtained at random in the Mystery Box (Cost: 950)
Give a russian vodka and a gun
disco stick
Any gun that shoots, cause its not like nazi zombies.