I posted in the "tissue damage" post and included some pictures of a sow I killed with my .308. I shoot 168 boat tail hollow point match bullets. They seem to blow up pretty well. If I was going to pay to shoot pigs somewhere and absolutely wanted to knock one down I would shoot a partition at 180 grains.
If you aren't serious about it, or not paying to hunt somewhere anything will be fine. I killed two this afternoon with a head shot from my .22 rifle. They are about on the same level as shooting at crows to me. They just leave more crop damage. The 168s shoot right at .5MOA out of my savage heavy barrel, and they are really cheap so thats what I load.