I have three predominant classes that I use out of my eight custom class slots.
Tank Mode
Primary: QBB-LSW w/ Foregrip, ACOG, FMJ
Secondary: RPG
Lethal: Frag
Tactical: None
Perks: Flak Jacket, Toughness, Tactical Mask
I have played Headquarters on many maps and gone 94 Kills 24 Deaths with this Class. Scorestreaks I tend to use with this class are: Orbital VSAT, Lodestar, K9 Unit or Swarm on open maps.
Snatch & Grab
Primary: Skorpion EVO w/ Quickdraw, Supressor
Secondary: KAP-40 w/ Dual Wield
Lethal: Combat Axe
Tactical: Flash Bang
Perks: Lightweight, Fast Hands, Dead Silence
Scorestreaks: UAV, Hunter Killer, C-UAV
Pointman
Primary: M27 w/Quickdraw, Fast Mag, FMJ
Secondary: SMAW
Lethal: Semtex
Perks: Blind Eye, Hardline, Cold Blood, Dead Silence or Engineer
Scorestreaks depend upon the people I am playing with for this class. But I can use this class on any map and come top three everytime in TDM, Kill Confirmed much to the annoyance of people who hump the MP7 !