Vitals are the way to go. It's about 100 times the size and will kill the pig just about every time. Neck shots are hit or miss; there's a lot of meat and few arteries, meaning the pig has a good chance of surviving. Stick with the tried-and-true vitals. You really cannot beat them too in the speed at which a vital shot will kill. I've seen neck shot kill just as fast but more often they took a while for the animal to bleed to death, whereas a shot to the vitals causes quick blood loss resulting in lack of oxegen to the brain. Thats why the animal will typically fall down within a moment.
I prefer neck. You have spine as well as the arteries. I will also put an arrow right behind a pigs ear into the brain if given the opportunity. This was a neck shot from a couple of weeks ago. I still have some of this one in the freezer!
Sorry wrong pic. Just look up my post, "Bowshot sow for the smoker".