I have two that have proven to be effective in getting fucking high points ....
 
1- Perks: Bling Pro, Stopping Power Pro, Steady Aim Pro
  Weapons : MP45 silenced with rapid fire, AA12 with a holder and red dot
Killstreaks: Predator Missile , Harriers, AC130
 
2- Perks : Marathon Pro, Stopping Power Pro, Commando Pro
Weapons : MP45 silenced and ranger or 1987 Akimbo
Killstreaks: Predator Missile , Harriers, AC130 

My favourite setup:
 
ACR with ACOG Scope
SPAS-12 with Grip
Seight of Hand Pro
Hardline Pro
Commando Pro
 
Then I usually have UAV, Care Package and Attack Helicopter.

I change my weapons all the time, I don't like playing with the same thing over and over... 
 
Just now though I'm rocking with: 
 
Vector w/ Silencer 
Spas-12 w/ Grip 
Marathon Pro 
Cold Blooded Pro 
NinJa Pro

Rapid Fire? Really?

I always change my set up, im trying to get all the emblems and titles. 
But for the moment.
mini uzi With red dot
marathon pro
lightweight pro
sitrep pro
 
harriers
pavelow
chopper gunner

" Rapid Fire? Really? "

At the moment... 
 
Scar w/ Silencer 
The L4D Shotgun (Can't remember the name.) w/ Silencer 
Scavenger Pro 
Cold Blooded Pro 
Ninja Pro

I have 3 primary builds. Pretty standard stuff.
 
Assult:
MW: Tar with FMJ (You can´t ring the dinner bell with silencer)
SW: Spas 12 with fmj (Grip does nothing)
1P: Sleight of Hand Pro
2P: Stopping Power Pro
3P: Ninja Pro (Always Ninja Pro)
 
Sniper:
MW: Intervention fmj (im on the train that says intervention just feels better)
SW: Akimbo M9: Now once you get your trigger finger down these babies rock. Generally is better suited for agressive than waiting since you need the jump on all the shotty spammers out there. however a 2 hit kill is nothing to frown uppon. Quick scope the arm??? no problem switch and kill the guy easily up close. Saves your life
perks (Sleight Pro, STP, NP) usual sniper build
 
Rush:
MW: Ump with silencer
SW: Akimbo Magnums (2 hit kill without stopping power and fast swap)
1P: Marathon Pro
2P: Coldblooded Pro for Pubs (Massive ammount of air support on xbox) Lightweight Pro in team games
3P: Ninja Pro

Oh wow. It's way too late for me to remember all my classes, but here are two I use to piss people off. 
 
 
Weapons:
     Primary  - Uzi w/ rapid fire (don't use) 
     Secondary - Model 1887 akimbo. 
Perks: 
     Perk 1 - Marathon Pro 
     Perk 2 - Lightweight Pro 
     Perk 3 - Commando pro 
 
Killstreaks: Predator Missile - Harriers - AC-130 (alt. Care Package - Predator Missile - Emergency Airdrop) 
 
Weapons :
     Primary  - F200 w/ M203 
     Secondary - void 
Perks: 
    One Man Army Pro 
    Danger Close Pro 
    Commando Pro 
 
Killstreaks - Harriers (alt. Pavelow) - Chopper Gunner - Tactical Nuke. 
 
 
I like to piss people off.

Mini-Uzi with the ACOG 
Dual M9s 
Marathon Pro 
Hardline Pro 
Ninja Pro 
Killstreaks: Care Package, Harrier Strike, Emergency Drop 

@lead_farmer  
 
YEAH M9S! 
 
Intervention 
Akimbo M9s 
 
Slight of hand pro
Stopping power pro
Steady Aim pro

M4 RDS
USP 45 w/ tac knife
 
Scavenger
Stopping Power
Commando
 
UAV
Precision
Pave Low

" Marathon Pro, Stopping Power Pro, Commando Pro "

I like to use:
Sleight of hand, stopping power, and steady aim
M16  w/red dot
Stinger
care package, predator missile, and emergency airdrop

my perks are:
 
eject
trade in
new game
 
no but seriously the perks are ridiculous in that game. same 3 setups are always being run. and its the fault of the developers for making them overpowered. but dont even get me started on the attachments.... heartbeat sensor... really?!?!?

" my perks are:  eject trade in new game  no but seriously the perks are ridiculous in that game. same 3 setups are always being run. and its the fault of the developers for making them overpowered. but dont even get me started on the attachments.... heartbeat sensor... really?!?!? "

My Master Key Class 
 
Marathon Pro 
Cold Blooded Pro
Ninja Pro

A few of my favorite classes.
1. Intervention-FMJ
 Secondary: Akimbo G18 or Usp's
   -Slight of Hand Pro
   -Stopping Power Pro
   -Steady Aim Pro
2. ACR- Red Dot
Secondary: AA-12 or Usp Tac-knife
   - Scavanger Pro
   -Stopping Power Pro
   -Ninja Pro/Commando Pro
3. UMP-Silencer
Secondary: Usp Tac-knife
   -Marathon Pro
   -Hardline Pro
   -Commando Pro
4. Tar-21-Silencer
Secondary- AA-12 or Usp Tac-knife
   -Scavanger Pro
   -Stopping Power Pro
   -Ninja Pro
 
 
Edit: Killstreaks
 Predator-Harrier-AC130/Chopper/Pavelow

3 basic classes usually work for me: 
 
1. Sniping (if you can call it that) 
Intervention FMJ/SPAZ-12 FMJ 
Semtex (or throwing knife)/Flash
Sleight of Hand Pro 
Stopping Power Pro 
Steady Aim Pro  
 
2. SMG 
UMP/P90 with PP2000/TMP 
Semtex/Flash 
Marathon 
Stopping Power 
Ninja Pro 
 
3. Assault 
SCAR/M16 with anything, really 
Semtex/Flash 
Scavenger Pro 
Stopping Power 
Ninja Pro 
 
And any of the stopping power perks can be switched with lightweight or cold blodded, and any of the first perks can be switched with marathon. It really depends upon what you feel like doing (rushing, quickscoping, slow and strong, etc.).

The ones that allow me to efficiently camp and get a 25 killstreak for a nuke.

" The ones that allow me to efficiently camp and get a 25 killstreak for a nuke. "

1. Intervention (FMJ) 
 USP.45 (Tact Knife) 
Throwing Knife
Stun Grenade

SoH Pro
SP Pro
Ninja Pro
 
2. Scar-H (Extended Mags)
USP.45 (Tact Knife)
Claymores
Stun Grenade
 
Scavenger Pro
SP Pro
Ninja Pro

" i didnt know that rapid fire made your gun inaccuarate. "

I only play Hardcore S&D so,
 
Primary Weapon: ACR with silencer. 
Secondary Weapon: Desert Eagle.
 
Perks: Slight Of Hand Pro, Cold Blooded Pro & Ninja Pro.

Marathon
Lightweight
Ninja
 
kill streaks predator/harrior/chopper gunner.....

Normally i stick to: 
 
Scavenger 
Stopping Power  
Ninja  
  
Are usually what i use for perks but ive started using Sit Rep and its kept me from getting killed in alot of stupid ways and also got me some kills cause i know when i see that claymore theres someone in that room waiting for the boom. 
 
I usually stick to either the M16, Acr, Intervention and the Scar with the Spas-12 as a backup but iam trying some new things so ive started using the Barret and the Styer. 
And my Kill streaks are and will always be Predator, Harrier, and AC-130  cause ive come to terms with and accepted the fact that i'll never get a nuke.

weapon- m16 red dot 
                 pp2000 fmg 
 
perks- stopping power pro 
             scavenger pro 
             steady aim pro 
kill streak-chopper, pavelow, chopper gunner

Perks: Sleight of Hand Pro, Stopping Power Pro, and I'm still experimenting with third perk.....right now I'm using Sit Rep. 
Deathstreak: Painkillers
Weapons: Tar-21 and G18 (don't have akimbo yet)

" Perks: Sleight of Hand Pro, Stopping Power Pro, and I'm still experimenting with third perk.....right now I'm using Sit Rep.  Deathstreak: PainkillersWeapons: Tar-21 and G18 (don't have akimbo yet) "

I mainly play Search and Destroy, so I use a sniping class. 
 
Primary: Intervention 
Secondary: Ranger Akimbo 
Equipment: Claymore 
Perks: Iron Lung, Cold Blooded, and Marathon 
Death Streak: Copycat 
Kill Streaks: UAV, Care Package, Predator Missile

My mains
 
M4A1 w/ Holographic Sight
USP .45 w/ Tactical Knife
 
P1  Scavanger Pro
P2  Stopping Power Pro
P3  Commando Pro
DS  Final Stand
 
--------------------------------------------
 
UMP  w/ Silencer and FMJ 
USP .45 w/ Tactical Knife
  
P1  Bling
P2  Hardline Pro
P3  Ninja Pro
DS  Martydom

 KSR: UAV, Predator Missle, Emergency Airdrop

" GUNNER: 
ACR (fall camo): red dot
Glock: FMJ
P1: sleight of hand
P2: stopping power pro
P3: commando pro
DS: painkiller 

RECON:
UMP (red tiger): silencer
PP2000: silencer
P1: sleight of hand
P2: cold blooded pro
P3: ninja pro
DS: painkiller

JARHEAD:
AK47 (urban camo): iron sight
SPAS 12: grip
P1: sleight of hand
P2: stopping power pro
P3: steady aim pro
DS: final stand
 
 
Oh yeah!  My killstreak setup:
5: predator missile
7: harrier 
11: AC130 "

ACR: silencer
Magnum: Knife
P1: marathon pro
P2: lightweight pro
P3: commando pro
DS: final stand 
 
ACR: Silencer and Red dot
Spas-12: Grip
P1: bling pro
P2: cold blooded pro
P3: ninja pro 
DS: final stand
 
Killstreak set:
7 Harrier
11 Chopper Gunner
25 Tactical Nuke
 

Perks & setup depends all on the gamemode & objective you play. In SnD I use the first killstreaks. When I play FFA or TDM I only use high killstreaks.  
Little video from myself, killstreaks are all in the description. (More on my channel)  

" @MONKEYFIST said:

" GUNNER: 
ACR (fall camo): red dot
Glock: FMJ
P1: sleight of hand
P2: stopping power pro
P3: commando pro
DS: painkiller 

RECON:
UMP (red tiger): silencer
PP2000: silencer
P1: sleight of hand
P2: cold blooded pro
P3: ninja pro
DS: painkiller

JARHEAD:
AK47 (urban camo): iron sight
SPAS 12: grip
P1: sleight of hand
P2: stopping power pro
P3: steady aim pro
DS: final stand
 
 
Oh yeah!  My killstreak setup:
5: predator missile
7: harrier 
11: AC130 "

This set up is full of WIN . Though you may wanna try ACR with the scope it will kill off from unbelievable distance with this gun's deadly accuracy "

I have different classes, but the one I use the most...
 
Primary Weapon: UMP 45 with silencer
Secondary Weapon: AA-12 Shotgun
Equipment: Semtex and Stun Grenades
 
Perks:

• Marathon
• Stopping Power
• Ninja

right now i'm using m240 with grip and red dot sight. 
 
bling pro
stopping power
commando pro. 
 commando pro is the only third perk i use. i think the rest of them are kind of useless. for killstreak i use UAV, care package and predator missile.  i use the grip on all my LMG's because it is a must have . i'm working on getting emblems and titles for my weapons.

I usually use 
 
Sleight of Hand Pro, Stopping Power Pro, and Commando Pro 
 with 
Scar 
with 
FMJ 
 
Works great for me most of the time and is pretty typical. I like to use that same setup with the AK-47 too tho sometimes.

Lately I've realized that the H-BAR seems to be more accurate than it should. That, given its relatively quick reload time makes it almost in between and assault rifle and LMG. So recently I've been:
 
Weapons: AUG H-BAR (Grip, FMJ)
                   SPAS (Grip, FMJ)
Perks: Bling Pro, Stopping Power Pro, Steady Aim Pro  
 
Alternatlively, swap Bling for scavenger with claymores and get rid of the FMJ