They are fairly accurate while standing still or in close quarters. They don't see much action unless your other weapons are empty, though. All classes can choose the shotgun. Good damage at close range, weak from a distance. Good weapon to finish an enemy off.
All classes can choose a submachine gun.
When crouched they provide decent accuracy and are best used at closer ranges. Recon class can choose the sniper rifle. You should be able to take out a Recon or Assault class with a well-placed headshot. Support classes will need a couple shots to finish off. Assault and Support classes can choose an automatic rifle.