I use both just as much. It depends on what mode I'm in. If I'm in sneaky mode then I use silencer although if I'm in rambo mode then I use high volume and the silencer off.
I don't really care about the pros. and cons. of the silencer, I personally think they're equal. It's not like the gun gets special powers by using silencer... if so, it shouldn't be like that. Just less sound should be made when firing with the silencer on, makes it realistic and powerful for stealth ambushes and/or attacks.