Ok, first your class:

Barrett .50cal/MSR Extended Mags & Speed or Impact

Five Seven Akimbo

C4/Throwing Knife

Sleight of Hand

Quickdraw

Any 3rd Perk

Ok Barrett or MSR, I have both classes Barrett w/ C4 because the .50cal is good at close range w/ Steady Aim so I can have explosives incase I need some. MSR w/ throwing Knife so if run outta ammo I can throw that fast or switch to the 57's (Dead Silence-Rush)

Killstreaks-UAV Ballistic Vests a great combo

You can be scoped in for 2 seconds and its still classifled as a quickscope.

As for your class

MSR with speed, extended mags or varible zoom or L118A Impact, extended mags

Sieght of Hand

Quickdraw

marksman or dead slience.

Have your sensitivty on 5-8 it works the best. try to keep a low profile....It will help keep you alive.