Given your parameters, the shotgun with 3 1/2 inch 00 buck shells is hands down the most deadly. 00 buck pellets are about .32 caliber. A 3 1/2 would have to carry at least 20 pellets.

Of course, shot placement is key to anything being effective. With a center of mass point of aim, within range, cylinder bore choke, the buckshot will put at least a dozen .32 caliber pellets in your target if not more. Everything else puts one projectile in the target.