Generally speaking, factory ammo being used, the most powerful would be the .44 mag. Now if you handload, you can do amazing things with the 45 colt, but it still isn't a .44 mag, although it does make a sizeable entrance hole.
If you are a handloader, then either a 45 colt or 44 magnum would handle even the biggest and baddest of hogs if your shot is placed where it needs to be placed. If you are not a handloader, then the .44 mag offers a greater variety of suitable factory ammo for hog hunting. Prices for the ammo can get steep though.
The .357 mag, while a nice powerful caliber is not up there with the other two. It can harvest hogs, but I think the margin or error is a bit smaller with it than the others.
markc
