I've got a few classes on the go, my main one is:
Proximity Alarm (rank3),
Stealth Enhance,
Rapid Fire
I'm using an unsilenced Marshall for this class as well as a Majestic and a Frag nade. This class is AWESOME for specter kills (Due to proxy alarm).
My secondary classes are more varied:
Grendel (Silencer, Red Dot Sight), Hammer (Silencer)
Proxy Alarm
Blind Spot
Mobility enhance
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Grendel (Assault Scope, Shotgun attachment), Hammer (Extended Mag)
Energy Transfer
Visor Enhance
Weapon Pro
My other class slots are used for experimentation and grinding other modules. I know I said varied but the Grendel is an awsome weapon and I challenge anyone to say otherwise