I'd go one step further and say whatever you have on hand that you can shoot accurately. The less the killing power, the more accurate it needs to be. For instance, even a .22 Hornet is instant death on even the biggest hog IF you can place the shot behind the ear. That same caliber in a heart/lung shot is inadequate for anything but very small hogs. .223 is a little better, but you still need precise placement to get that ear shot. Moving up to more power, allows a little more leeway.Best Hog killing gun/caliber? Whatever is at hand.