Well it mainly depends on how you play

and your rank of course

Let's see, one of the best silencable pistols would be the USP, (imo) due to the little recoil and relatively good power, it's open from the start and can be fired pretty quickly too if ya know how to use it.
The M9 is ok, i havent spent too much time with it but it's an okish pistol, but it can be twitchy, with times getting a large amount of kills, and others getting hardly any.
As soon as you get the Desert Eagle, you wont want to use any of those previous guns much, maybe only on stealth classes, due to the high power in close proximity, making it 2 / 3 shots a kill.
In short though, If you want a pistol that can be used in longish range with decent accuracy, stick with the M9 or the Usp (silenced or unsilenced, again depends on play style) but if you want your pistol for anything close or medium range stick to the Deagle or when Low leveled the usp or m9 again

Hope i helped.. a bit?