go commando and use one of the top 3 machine guns with martydom and bouncing betty. use any pistol. shoot all enemies (quite easy) and place landmines on the flags. also, when ur about to die and they're collecting flag, go near for martydom, hopefully 30 seconds will be finished. fall down on one of the enemy flags.
Assassin with sniper=good at long range,1 hit kill
Assassin with melee wep=lose range is very deadly, useless at long range apart from secondary wep
Medic with assault rifle=good at close range
Medic with magnum=good at medium range 3/4 shot kills
Commando with machine gun=very powerful at close range
Commando with grenade launcher=make sure enemy is below or better aiming
Commando with rocket launcher=good for throwing rockets from long range
Tank with shotgun=close range or all the shots to hit
Tank with shield and secondary wep=close range is better as accuracy is lower with shield