you should use the shotgun dude its much better but you have to get in real close. the other ones you have to counter the recoil so aiming is much harder. use the BAR or Stg88 when you are further away from your enemies because they have longer range. use the smgs when your closer.
Every map/situation/objective has it's appropriate weapon. Ultimately (he said with a wincing grin) you should pick a weapon suited to your goal and then counter that with what the other guys in your team are using. We all know how little 'team' play there is, but if everyone is using SMG's, try a MMG like the BAR or even, yes, even a sniper rifle or M1/Kar to reach out a little and give longer range support. If everyone is running around with rockets, SHOOT THEM!... seriously, pick the weapon best suited to the mission and to balance what others are using. JMO
On close combat maps like Stalingrad the StG is much better but it's useless on long distance (OK not useless but not so good). The BAR rifle is awesome at distance. In Omaha you can "snipe" people on the top from the beach with just a few shots.