Depends on the situation, really.
If we're gonna be hopping into trenches via the flanks to clear out the japaneses or flush them out of the bushes in Guadalcanal, I use the trenchie.
If we're going to assault buildings or other places where one would expect to spray a lot from the hip, I'd use the tommy with the drum mags.
If it's going to be a wierd mishmash of both of these or there's going to be a lot more range involved, I'd go with the carbine.