Can't beat a silenced 22 in the noise department but then you run into the question.... is the 22 a strong enough round to use on a important job. Personally i don't think it is and if you want to use a silencer equipt piece i'd go with a silenced 9mm or maybe even a silenced 45. Even a .380 auto round is better then a 22 in my opinion.

But then again you run into the problem of possible jamming with any of the auto handguns. But if noise is a concern you might have to use one since you can't use a silencer with a revolver. It just won't work because of the escaping gases between the cylinder and the barrel.