In defiance of the logic learned during my thousands of plays of Zombie Quest 4: Leon's Big Adventure, the shotgun is not for mobs of zombies, but rather for big ones. The pump shotgun is good enough to kill hunters and smokers at medium/close range before they can do real damage and, more to the point, the auto shotgun actually does appreciable damage to the tank, unlike the assault rifle, which takes way, way, way too long. At the end-of-level "tankbuster" rankings it's always the ones with the auto shotgun who have over 2k damage done.
That said, i really like the sniper rifle. It's probably the worst weapon for late-game hordes and i never take it in the finale -- though if you get a long hallway where the horde's coming straight at you, the amazing damage and material penetration of the rifle can let you take out 5-6 enemies in one shot -- but it is a fantastic solution to groups of distant enemies, allows assault rifle-wielders to save their ammo on generic zombies in parking lots and such, and lets you deal with smokers, hunters (assuming you can see them before they pounce) and, most importantly, poorly-placed witches. Without a sniper rifle, a witch in front of the safehouse door is some serious shit, and someone basically will have to draw the short straw and just get stomped; WITH a sniper rifle in the group, witches don't usually get to do any damage at all.
