I personally use these five customs classes:
1. Assault
Primary weapon: M16 + ACOG Scope + Digital camouflage
Handgun: Desert Eagle
Grenades: Flash
Perk One: 3x Frag
Perk Two: Stopping Power
Perk Three: Martyrdom
2. Heavy Weapons
Primary weapon: RPD + Grip + Digital camouflage
Handgun: Desert Eagle
Grenades: Flash
Perk One: (occupied by Grip for RPD)
Perk Two: Stopping Power
Perk Three: Deep Impact
3. Stealth Ops
Primary weapon: G36C + Silencer + Digital camouflage
Handgun: M9 + Silencer
Grenades: Smoke
Perk One: 2x Claymore
Perk Two: UAV Jammer
Perk Three: Dead Silence
4. Sniper
Primary weapon: Dragunov
Handgun: Desert Eagle
Grenades: Smoke
Perk One: 2x Claymore
Perk Two: Stopping Power
Perk Three: Martyrdom
5. Speed Demon
Primary weapon: Scorpion + Laser Aim
Handgun: Desert Eagle
Grenades: Stun
Perk One: 3x Stun
Perk Two: Extreme Conditioning
Perk Three: Sleight of Hand
I use Stealth Ops on dark levels with a lot of cover (especially Downpour, Bloc, Wetwork, District and sometimes Pipeline), Heavy Weapons on small maps with no danger of snipers (Showdown, Vacant and exceptionally Bog - this one has a high danger of snipers, but LMG's with high accuracy (preferably with Grip and Steady Aim) are extremely useful on this map
) and Assault on all others 'average' maps (Crossfire, Strike, Crash, etc.). Oh, and Sniper on Overgrown
.
Speed Demon is extremely fast (as my name implies, haha), but my reaction time makes it the least used class. Still, throwing a stun grenade in a room full of enemies then sprinting behind their backs and taking them all out is a lot of fun.
P.S.: This post is way longer than it should be ... I should be learning ...