Carbine, definatly the carbine. has a high fire rate, does good damage, higher number of shots then the battle rifle, but not as common on maps :(.
As for energy sword or shotgun, definatly the shotgun. if u have the sword and come up against someone half decent with a shotgun your toast, no matter what. lunge=they shoot u in the face. run away = they shoot you anyway. and anyway, even if u dont kill someone with your first shot of the shotgun, a quick melee usualy finishes the job!