There are four main types of classes that can be created in MW2. Runner is a light fast agile class that gets into enemy territory and attacks from a short range. Sniper, as the name suggests, is a long distant patient slow but deadly class. Stealth goes by undetected and kills enemies without alerting the rest of the team. Tank is a slow deadly class that can handle large groups of enemies at a time.
Runner[edit]
Only use SMGs for this class. You can play around with each of them to find one that suites you best, they are all effective and in their own special way. Use FMJ attachment as you'll probably want to ensure your enemies die quickly as you'll be out of ammo quickly due to high fire rates, delay and general enemy movement. Perks such as commando, light weight, marathon and sleight of hand are perfect for this class. remember you'll be close to your enemies so a knife can be very handy.