Call of Duty: Modern Warfare 2 Multiplayer Guide
Perks show up here for your selection as they unlock.
Perks are the main way your in-game character can be different from others in the match, because perks can be combined in many different ways to suit your play style. Once you’ve reached Level 4 and unlocked Create-a-class, you can begin experimenting with various perk combinations to find which you like best and how different perks compliment each other when used together. While some perks are very effective on their own, things get really interesting when you combine your choices in each of the three perk slots along with your Killstreak and Deathstreak rewards and your weapon choices. Certain perks suit given weapons better than others. For example, Lightweight makes you move faster than you normally would with whatever weapon you chose, but if you happen to be using one of the SMGs, which along with the Sniper rifles give you the greatest mobility, you will be faster than any other player not using the same combo. If you then combine Lightweight, a mobile class, and Marathon, you can really fly around the map.
As you complete matches with any given perk in use, you work toward unlocking the Pro version, which adds something to make that perk more effective. Progress can be tracked by selecting the perk in the Create Class menu until you have completed the challenge and earned the Pro version. Remember that you only earn Pro credit by performing the required skill WITH that perk applied. For example, sprinting without Marathon chosen as a perk does not earn mileage toward unlocking Marathon Pro, and melee kills without Commando applied do not earn credit toward Commando Pro.
Until you unlock a good selection of perks, the default classes offer pretty good options.