There are soooo many to choose from....most shotguns,most sub machine guns most....well you know how it goes

Hands down it is the underslung shotgun attachment. That thing is flat-out terrible. It combines all the worst parts of the shotguns in MW3 in the convient pump-action 4 shell magazine.

Whoever thought having to get 40 kills with that to complete the challenge, but only doing 15 with the silencer was a good idea, I would like to smack them with a spoon repeatedly. It is absolute torture trying to finish all the challenges for ARs because I know the shotgun attachment is always there, mocking me.