Just thought I'd add this. Last night on a ps3 private match, 3 of us playing, a guy got rid of his ppsh for a flamethrower, I told him keep the gun but he said he had no ammo. I was also low on ammo, so went to the box right after, and got a flamethrower too. Back to back flamethrowers!! I also saw 2 flamethrowers on 4player verruckt, but split screen we could never get 2.
Wunder gun - get a crowd of zombies almost on top of you, shoot the wonder gun, and you'll be ok. Any other gun, you'll die. That's it's strength. Raygun you'll kill yourself, and bullets wont suffice when it's too late.
I also noticed flamethrower not nearly as effective power wise. It also seems the speed you walk at when carrying the flamethrower is way down. Seemed strongest in verruckt to me.