Here's a class i use in FFA, Im in the top 300 for it.
Honeybadger, red dot, foregrip
Quickdraw, Sleight of hand, Dead silence, Amplify, Focus, Blast shield
Strike package Assault
I.M.S, Sentry gun, Helo Pilot
Another setup i use alot is the Remington Assault rifle with red dot and Armor Piercing rounds.
Hopefully this helped on raising your kdr and wl.
I currently hold a 4.2 kd and 3.7 wl
Good luck bud!
(update)
Do not use the ARX it is the worst assault rifle in the game. It has terrible recoil.
Use the Honey badger, Remington, Mtar-x, Maverick, sc-2010,