I've shot quite a few hogs with the .223/5.56, not because I think it's the best caliber for the purpose, but that's what I'm issued for work.
While I agree that shot placement is important, when you come up on a sounder of hogs you MIGHT have a chance for surgical placement of the first round, after that you'll be shooting at animals that are running, bouncing and pretty much presenting only their hind ends as targets.
Even the best .223 bullets aren't really adequate to anchor a hog much over 50 pounds with a shot in the butt. A light, highly frangible varmint bullet is likely to create a shallow, gory wound that won't anchor even a small pig and will more often than not cause it to die days later from infection.
When walking up hogs on my own time, I prefer to use my .308 M1a and a 20 round mag loaded with 150 or 165 grain Partitions. Even on large hogs they're able to smash the hip and still penetrate through the gut cavity to reach the lungs and heart for a quick, sure kill.
I heartily dislike feral hogs, but no creature should be made to suffer needlessly. Besides, they taste a lot better when they haven't run a half mile with adrenaline and gut contents tainting the meat.
Not to hijack the thread, but diseases carried by feral hogs can be dangerous to humans if proper precautions aren't taken. I'd urge anyone going out after hogs to check out the links below.
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5822a3.htm?mobile=nocontent
http://feralhogs.tamu.edu/files/2011/08/Feral-Hogs-and-Disease-Concerns.pdf
http://www.tpwd.state.tx.us/huntwild/wild/nuisance/feral_hogs/