(This is my opinion, you also have a right to your opinion, so don't go crazy on me.)
Step 1: Primary Gun
I will have a breakdown on the guns
Snipers: +Range +Power -Defensive +Offensive Recommended: PSG1 or L96
Shotguns:-Range +Power +Close Range Defense+Close Range Offense Recommended: SPAS-12
Assualt Rifles: +Range +Power -Recoil +Offense Defense depends
Submachine Guns -Range +Power with rapid fire -Recoil +Defensive gun Recommended: AK74u or MP5K
LMGs:+Range +Power -Recoil -Reload Recommended: Stoner63
Note: By defensive and offense I mean if you started the gunfight or are defending from the gunfight.
Step 2: Secondary Gun
Pistols: Can be effective or terrible, depending how you use them. Recommended: C275 Full Auto or Python Speed Reloader
Launchers: These can be effective for non-flak jacket opponents, and enemy air support.(Easy Points) Recommended: M172 Law
Specials: Because these are so different, I am giving them their own section
Crossbow: This is great for stealth, because you don't appear on the radar, and you can get an instant kill with certain accuracy
Ballistic Knife: Hard to use, no iron sights. Aim above your target
Step 3: Perk 1
Lightweight Pro : Sprint Faster + No Falling Damage. You can take advantage for no falling damage, like escaping out of a window.
Flak Jacket Pro : Reduced Explosive Damage + Reduced Flame Damage. Great for capturing objectives in Dom. Helpful for Noob Tube and Grenade Spamming
Scavenger Pro: Take ammo from fallen enemies + More Starting Ammo. You can use this with a high-rate-of-fire submachine gun. Very helpful for high killstreaks.
Hardline Pro: 1 less kill required for killstreak + Can reroll care packages. You should use this with the care package. Rerolling for 5 killstreaks and below is recommended.
Ghost Pro: Remain hidden from spy planes + Avoid attack helicopters, no red diamond from chopper gunner and gunship. No name appears when aimed on. Use this class to stealth around and flank. Don't forget your supressor.