The AK103 7.62mm is the most powerful assault-rifle in the game. It has a low rate of fire, and high recoil penalty. It is most effective at medium range, used in bursts of 2-5 rounds. It is very effective at close to meduim range, where it can outgun pretty much any other weapon in the game. Also it features a low rate of fire allowing for ammo conservation. In the 4.2 release of Urban Terror the laser sight has been disabled on the AK-103.
The Ak is best viewed rather as an automatic rifle, than as an assault rifle. Its single shot mode (when walking) is very accurate and deadly over the long range (Riyadh). At close range (Turnpike, Abbey and Dressingroom) the spread from automatic mode is still within tolerance and the high damage per second allows the shooter to kill quickly, and often before one gets hurt.
However the rifle has worse cards at medium range than G36 and other 5.56 rifles. Too small rate of fire in single shot mode and significant spread in automatic mode lead to lower effective damage per second. It may loose first shot advantage against HK G36 on long range, because it lacks scope.