Attachments: Select fire - Suppressor
Perk 1: Lightweight
Perk 2: Fast hands
Perk 3: Engineer
Tactical: Tactical insertion
Perfect class for SnD and objective gamemodes. Swat-556 kicks ass on range, but lacks the speed up close, that's why I use the select fire to switch to that 937,5 RPM automatic. The Five-seven is awesome while having a trigger finger.
C4 is great for clearing out a camper or to defend a objective. The tactical insertion (combined with fast hands) allows picking spawn points near the objective.
Show some love to the Swat-556, it's a hidden diamond within the assault rifles. Crazy accuracy, high damage and the select fire makes it usable on all ranges.
Here's the class that has been working out well for me recently:
Attachment(s): Silencer, Grip, Quickdraw Handle
Perk(s): Hardline, Ghost, Toughness, Dexterity
Scorestreaks: Stealth Chopper, Orbital VSAT, Escort Drone
Wildcards: Perk 1 Greed, Primary Gunfighter
I hope this helped!