Indiana used to be shotgun and muzzleloader only for deer. As a result, I've shot a fair number of both deer and hogs with shotgun slugs, mostly out of a 12 gauge with a rifled barrel.
I never did any accuracy testing, but the general consensus among deer hunters here was that rifled slugs shot best in smooth bores and that sabots shot best in rifled barrels.
I have used a smooth bore 20 gauge with Winchester rifled slugs, worked fine at 50 yards and in.
Any well placed slug, 20 or 12 gauge, is going to be devastating on a hog sized animal. I'd buy the cheap slugs, and if you can hit a pie plate at 50 yards you're good to go.
The nice thing about hogs is that as long as they don't smell you, you can usually walk right in close to them.