Setups:

Default: M4A1 Red dot + Akimbo G18
Marathon Pro, ﾃつ*Stopping power Pro & Ninja Pro

AntiSniper: Scar-H Thermal + Stinger
Scavenger Pro, Cold blooded & Ninja Pro

Spray: Silenced MP5 + Red dot M93
Marathon Pro, ﾃつ*Lightweight Pro & Ninja Pro

The default setup is awesome for maps like Karachi, Invasion, Skidrow, Rundown and such. I use my default setup for most maps. The M4 offers long ranged stopping power, without too much recoil. I mainly use the G18s for cleaning buildings and narrow streets. This is a good all-round class, which I use a lot.

I mainly use my anti-sniper setup on maps like Wasteland and the rainy maps, where are thermal scope is a real must-have. Snipers tend to spam Killstreak-awards a lot, and on the open maps, these are usually very effective. That's why I like the stinger as secondary. Because the Scar is quite quickly out of bullets, I use Scavenger Pro.

For real spraymaps like Rust, Terminal and Scrapyard, I really need the extra speed, so I use Marathon & lightweight. The silenced MP5 for short range spraying, and the M93 with red-dot if I spot an easy mid-range kill. Spray 'n run.