Until recently, one of my priorities at the beginning of each campaign (always in Expert) was to find the autoshotgun. Its firepower and ease of use left its “poor sister” in a bad place. That's why I was surprised that some of my campaign comrades, especially the Russians, insisted on using the pump until the end. This pushed me to find out on my own why the best l4d players in Expert prefer the pump over the auto. And I found out: the “pump” gives you a feeling of authenticity that the “auto” doesn't. The sensation that comes from “fighting” a tank with the “pump” is impossible to obtain with the “auto”. The adrenaline rush you get when you reach the top of the Witch, knowing that you don't have the next quick shots and you are risking your neck, is not given to you by the “auto”. With the “auto” everything is easy and comfortable: without moving your finger on the trigger you can dispatch the horde simply by pointing at each thread. The same with the SI: if the first shot doesn't work by keeping your finger on the trigger, the second one is almost 100% sure to do so.

From my experience I can tell you that auto shotgun is not a tactical shotgun. The more I do not understand one of the shotguns in l4d2 called tactical. But back to the l4d: The pump shotgun is the only weapon, which is not spammy, and you can create tactics while shooting. This is the main reason why I always prefer pump, unless the server is poor latency.