180gr Accubonds in .308 win...or bigger
My answer is shoot whatever you feel is most accurate and reliable through the weapon. With a .223/5.56, I'd go with a shot to the nervous system. I've killed a bunch of pigs with my AR and had a few get away because of going for heart shots. My AR shoots accurate groups using surplus Lake City M855 Penetrator (62gr green tip) and I have a lot of them... and it kills pigs. I promise.
A lot of members of pig hunting forum I'm on suggests Barnes TSX when using a .223 but the topic is debated on weekly.
In my experience, the first shot counts the most and if you get follow up shots on the rest of the brood, you're a mixture lucky/good. After the first shot, when the chaos ensues, putting accurate shots (obviously needed with a .223) on running rooters between scrub and trees is a real challenge. I usually try to go for neck shots because they're easier shots than heart shots or shots to the grape, especially when the chaos starts. Because of the follow up shots, I like to have something with more punch. I've been thinking of deploying my M1 Garand because I get a fast rate of fire with a 30-06 round.
Pig hunting (to me) is much more fun than deer hunting. I've killed pigs with anything from a .22lr to a 12ga as well as having more than a few get away. Nine times out of ten, when one got/gets away it's due to my error but I found you minimize your margin of error by shooting a larger-more powerful round...
The AR is obviously an awesome weapons platform because of the rate of fire makes it possible to kill off entire broods. We started using a semi-auto 12ga with buckshot where we hunted in South Texas because the shots were within 40yds and we didn't usually clean or eat the pigs (they were usually big, nasty, taste like garbage and the land owner liked to see dead pigs drug out to the bone yard). In my opinion, nothing is more effective in exterminating pigs (other than helo's or trapping) than running up on group with a shotgun and a four wheeler. I think I may have a different outlook on "hog hunting" than others though.