What is the Best mw2 class

It depends on what you're good at. Here are some classes that I use:
TAR-21
Stinger
Semtex/Smoke
Scavenger/Stopping Power/Sit Rep
Martyrdom

UMP 45 Silenced
M93 Raffica
Claymore/Stun
Marathon/Cold-Blooded/Ninja
Martyrdom

L86 LSW w/ grip and Hearbeat sensor
AA-12 w/ Red Dot Sight
Semtex/Flash
Bling/Stopping Power/Commando
Martyrdom

Intervention w/ Heartbeat sensor
.44 Magnum Tactical knife
Semtex/Flash
Sleight of Hand/Lightweight/Steady Aim
Martyrdom

Riot Shield
Striker
Frag/Stun
Sleight of Hand/Hardline/Commando
Martyrdom

Note: I don't have Xbox Live, but I have played it before. And I'm only level 36, so these might not be the best