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
Give a russian vodka and a gun
The Ray Gun is only available in the Nazi Zombies mode and can be obtained at random in the Mystery Box (Cost: 950)
disco stick
Any gun that shoots, cause its not like nazi zombies.